Omniknight
* Jakiro's area-of-effect abilities that deal magical damsge make it hard for Omniknight to save multiple enemy heroes at once with 
Purification and 
Repel, and 
Guardian Angel and to harass Omniknight on lane.
* 
Aghanim's Scepter upgraded 
Macropyre allows Jakiro to deal pure damage and slow enemy heroes which can pierce debuff immunity, rendering both Repel and Guardian Angel useless.
Naga Siren
* Jakiro's damage over time abilities can clear Naga Siren's illusions and can hurt real Naga Siren even for the duration of 
Song of the Siren.
* Naga Siren is not a hero that likes to go for 
Black King Bar, and that makes her very vulnerable to Jakiro's damage over time in every phase of the game.
Additional:
* Jakiro's damage over time abilities can clear Naga Siren's illusions and can hurt real Naga Siren even for the duration of Song of the Siren.
* Since Naga Siren is a hero who barely goes for Black King Bar, this can make her very vulnerable to Jakiro's damage over time in every phase of the game.
Omniknight
* 
Mortimer Kisses can reduce Omniknight's impact in teamfights. Omniknight's 
Heavenly Grace cannot purge multiple stacks of Mortimer Kisses. The damage is also magical, making Omniknight's ultimate, Guardian Angel, useless.
Naga Siren
* Mortimer Kisses can make quick work of Naga Siren's illusions.
* 
Scatterblast and 
Firesnap Cookie's AoE damage are also decent ways to deal with Naga's illusions.
Omniknight
* Heroes under Guardian Angel can be still damaged from the pure damage of 
Black Hole and magical damage of 
Midnight Pulse.
Naga Siren
* Heroes with AoE nukes will clear her illusions in no time, especially if they are percentage-damage-based, like 
Underlord's 
Firestorm, 
Elder Titan's 
Earth Splitter, 
Enigma's Midnight Pulse, 
Zeus's 
Arc Lightning, 
Jakiro's 
Liquid Frost from 
Aghanim's Shard etc.
Omniknight
* Guardian Angel is generally useless against Lina as she primarily relies on magical damage. Lina can also dispel it with 
Eul's Scepter of Divinity as she is a hero who often goes for it. Eul's Scepter of Divinity can later be upgraded into 
Wind Waker, which will allow Lina to escape from Omniknight.
* 
Laguna Blade can often finish off Omniknight's allies before he can save them with Purification and Repel. This can become even worse once Lina picks Laguna Blade damage is pure and pierces spell immunity talent, which will allow it to ignore both, any form of spell immunity and Guardian Angel.
Naga Siren
* Heroes with summons and illusions can find themselves easily bested by Lina, like 
Broodmother, 
Nature's Prophet, 
Chen, 
Terrorblade, 
Naga Siren, 
Visage, 
Wraith King, 
Lycan, 
Phantom Lancer, 
Shadow Shaman.
Omniknight
* Guardian Angel does not offer protection from 
Eclipse, though it will negate damage from 
Moon Glaives.
* Luna's high magical damage from 
Lucent Beam and Eclipse can often finish allied heroes before Omniknight can save them with Purification.
* Likewise, Luna's high physical damage from Moon Glaives and 
Lunar Blessing is strong enough to counter debuff immunity from Repel.
Additional:
* Guardian Angel does not offer protection from Eclipse, though it will negate damage from Moon Glaives.
* Luna's high magical damage from Lucent Beam and Eclipse can often finish allied heroes before Omniknight can save them with Purification.
Naga Siren
* Luna's Moon Glaives and Lunar Blessing can clear waves of Naga Siren's illusions from 
Mirror Image.
* Once Naga Siren's illusions are cleared with Aghanim's Shard upgraded Moon Glaives, Eclipse can often finish off Naga Siren before she can escape with Song of the Siren.
* A well-timed Aghanim's Scepter upgraded Eclipse combined with 0.25 Eclipse Lucent Ministun talent can be casted at long range and allow Luna to burst down Naga Siren faster and repetively stun Naga Siren, preventing her from escaping with Song of the Siren and 
Town Portal Scroll without getting caught in it's range.
* Luna is a natural Black King Bar wielder unlike Naga Siren who barely goes for it, which allows Luna to freely attack Naga Siren during Song of the Siren and potentially get rid of the most of the damage and crowd-control from Naga Siren.
Additional:
* Luna's Moon Glaives and Lunar Blessing can clear waves of Naga Siren's illusions from Mirror Image, especially when combined with 
Gleipnir and 
Manta Style. Aghanim's Shard upgraded Moon Glaives can also be used to destroy Naga Siren's illusions and damage the real Naga Siren if they are too close to Luna while also reducing any damage Naga Siren inflicts on Luna for their duration.
* Once Naga Siren's illusions are cleared, Eclipse can often finish off Naga Siren before she can escape with Song of the Siren.
* A well-timed Aghanim's Scepter upgraded Eclipse combined with 0.25 Eclipse Lucent Ministun talent can be casted at long range and allow Luna to burst down Naga Siren faster and repetively stun Naga Siren, preventing her from escaping with Song of the Siren and Town Portal Scroll without getting caught in it's range.
* Luna is a natural Black King Bar wielder unlike Naga Siren who barely goes for it, which allows Luna to freely attack Naga Siren during Song of the Siren and potentially get rid of the most of the damage and crowd-control from Naga Siren.
Naga Siren
* Heroes that create illusions: 
Spectre, 
Shadow Demon, Phantom Lancer, Naga Siren, 
Chaos Knight, Terrorblade) or bring other units into the fight (such as Nature's Prophet, 
Lone Druid, Chen, 
Enchantress, 
Meepo and 
Arc Warden) can cause Eclipse to strike the illusions/summons unintentionally. However, in many cases Moon Glaives can resolve this issue and eliminate them before activating Eclipse, but that will require lots of farming for right-click items.
Omniknight
* Heroes who cannot escape from Trample early might be easy first blood. Heroes like 
Witch Doctor and 
Omniknight should play very cautiously alone...
Naga Siren
* Illusion heroes will struggle against Primal Beast's area damage capability, such as Chaos Knight, Naga Siren, Terrorblade.
Omniknight
* Heroes who can drain mana can make Omniknight useless after he uses one or two abilities: 
Lion, 
Anti-Mage, 
Nyx Assassin.
Naga Siren
* Lion may upgrade 
Mana Drain, 
Hex and 
Finger of Death through Talent Tree and Aghanim's itens to make them affect secondary targets or turn them into AoE abilities. This can make things difficult for heroes like Phantom Lancer, Naga Siren and Terrorblade, who rely on illusion armies.
Additional:
* Both Hex and Mana Drain destroy Naga Siren's illusions in an instant, making it hard for her to teamfight or push against a team with Lion. If Lion chooses the AoE effect talent for Hex or the shard for multi-target Mana Drain, it can negate her pushing potential entirely.
* 
Earth Spike is an AoE disable with good damage. If used well, it can help distinguish the true Naga Siren by the damage they take (illusions take more damage).
Omniknight
* 
Fortune's End's AoE dispel will remove Heavenly Grace and Guardian Angel.
Additional:
* Oracle can dispel Heavenly Grace (which he can also bait out with Fate's Edict).
* With Fortune's End, Oracle can dispel Guardian Angel in an area of effect.
Omniknight
* Heroes with long cooldowns on their abilities or ultimate will struggle against the relentless pressure provided by 
Fiend's Gate: Terrorblade, 
Dragon Knight, Omniknight.
Naga Siren
* 
Atrophy Aura makes it hard or Naga Siren to farm on lane and damage Underlord with 
Rip Tide in teamfights. And her only way to counter this is by playing Nuker role.
* Firestorm is very useful for clearing Naga Siren's illusions from Mirror Image and Manta Style.
* However, Naga Siren can catch Underlord and his team unprepared with Song of the Siren if he chooses to use Fiend's Gate to get to a designated point of the map. Naga Siren can also prevent escaping with Fiend's Gate with 
Ensnare and 
Reel In from Aghanim's Scepter.
Additional:
* Atrophy Aura makes it hard or Naga Siren to farm on lane and damage Underlord with Rip Tide in teamfights. And her only way to counter this is by playing Nuker role.
* Firestorm is very useful for clearing Naga Siren's illusions from Mirror Image and Manta Style.
* However, Naga Siren can catch Underlord and his team unprepared with Song of the Siren if he chooses to use Fiend's Gate to get to a designated point of the map. Naga Siren can also prevent escaping with Fiend's Gate with Ensnare and Reel In from Aghanim's Scepter.
Naga Siren
* Heroes with strong area-of-effect damaging and/or disabling abilities will be able to intercept Underlord and his team when they exit from Fiend's Gate: 
Luna's Aghanim's Scepter upgraded Eclipse, 
Dawnbreaker's 
Solar Guardian, 
Axe's 
Berserker's Call, 
Mars's 
Arena of Blood, Jakiro's Macropyre, 
Dual Breath and 
Ice Path, Naga Siren's Song of the Siren, 
Razor's 
Eye of the Storm and 
Plasma Field, 
Lina's 
Light Strike Array, Broodmother's 
Spinner's Snare from Aghanim's Scepter, Elder Titan's Earth Splitter and 
Echo Stomp, 
Alchemist's 
Unstable Concoction and 
Acid Spray, 
Queen of Pain's 
Sonic Wave, 
Dark Seer's 
Wall of Replica and 
Vacuum, 
Venomancer's 
Noxious Plague and 
Poison Nova from Aghanim's Scepter, 
Oracle's Fortune's End and 
Rain of Destiny from Aghanim's Shard, 
Bloodseeker's 
Blood Rite, Enigma's Black Hole and Midnight Pulse, 
Shadow Fiend's 
Requiem of Souls, 
Batrider's Aghanim's Scepter upgraded 
Flaming Lasso, 
Firefly, 
Flamebreak and 
Sticky Napalm, 
Ancient Apparition's 
Ice Blast, 
Sand King's 
Epicenter, 
Sand Storm and 
Burrowstrike, 
Gyrocopter's 
Call Down, 
Ember Spirit's 
Sleight of Fist, 
Death Prophet's 
Exorcism and 
Silence, 
Monkey King's 
Wukong's Command, 
Crystal Maiden's 
Freezing Field, 
Muerta's 
The Calling, 
Medusa's 
Stone Gaze, Zeus's 
Nimbus from Aghanim's Scepter. 
Dark Willow's 
Bramble Maze, 
Pangolier's 
Swashbuckle, 
Grimstroke's 
Soulbind, 
Ink Swell and 
Stroke of Fate, 
Earthshaker's 
Echo Slam and 
Fissure, 
Puck's 
Dream Coil and 
Waning Rift, 
Winter Wyvern's 
Winter's Curse, 
Magnus's 
Reverse Polarity.
Naga Siren
* Mirror Image's illusions increase Echo Slam's damage.
Additional:
* Earthshaker's strong AoE abilities can clear Naga Siren's illusions, or at least make it easier to distinguish the real one by the damage they take.
* Echo Slam deals more damage against more enemies, which can be devestating against Naga Siren and her illusions.
Naga Siren
* All of Leshrac's abilities, especially 
Pulse Nova, can easily deal with Naga Siren's illusions.
* Aghanim's Scepter gives Leshrac access to 
Nihilism ability, that allows him to turn himself along with Naga Siren and her illusions to turn ethereal. And to make things worse, Nihilism can slow Naga Siren and her illusions, make them more vulnerable to magical damage and unable to fight back while Leshrac moves faster and does not take increased magical damage for it's duration.
Omniknight
* 
Dispel Magic from {U:Storm} instantly removes Heavenly Grace and Guardian Angel from Omniknight's allies in its radius of effect.
Naga Siren
* Dawnbreaker can easily clear waves of Naga Siren's illusions from Mirror Image with 
Starbreaker, 
Celestial Hammer and Solar Guardian.
* Aghanim's Shard upgraded Starbreaker will allow Dawnbreaker to dispel Ensnare and freely attack Naga Siren during Song of the Siren when combined with Black King Bar, a common item on Dawnbreaker.
* Solar Guardian allows Dawnbreaker to counter any attempts of Naga Siren and rejoin her team with Solar Guardian when they require it. Aghanim's Scepter upgraded Solar Guardian can also give Dawnbreaker's allies evasion while Dawnbreaker is airborne for it's duration, as Naga Siren mainly relies on direct attacks in order to deal damage.
Additional:
* Dawnbreaker can easily clear waves of Naga Siren's illusions from Mirror Image with Starbreaker, Celestial Hammer and Solar Guardian.
* Aghanim's Shard upgraded Starbreaker will allow Dawnbreaker to dispel Ensnare and freely attack Naga Siren during Song of the Siren when combined with Black King Bar, a common item on Dawnbreaker.
* Solar Guardian allows Dawnbreaker to counter any pushing attempts of Naga Siren and rejoin her team with Solar Guardian when they require it. Aghanim's Scepter upgraded Solar Guardian can also give Dawnbreaker's allies evasion while Dawnbreaker is airborne for it's duration, as Naga Siren mainly relies on direct attacks in order to deal damage. Solar Guardian can also be used after Naga Siren uses Song of the Siren near her allies to either escape from or counter-initiate against them.
Omniknight
* 
Global Silence takes Omniknight out of the fight completely.
* 
Glaives of Wisdom are a great harass vs Omniknight during the laning stages of the game, since it doesn't aggro creeps & ignores his high base armor. It deals pure damage, which means it can also go through Guardian Angel.
* Silencer's intelligence steal can also cause Omniknight to falter in the early phases as it reduces his ability to use his spells.
Naga Siren
* Timbersaw's innate durability provided by 
Reactive Armor is very hard to deal with as Naga Siren as she mostly relies on sustained damage rather than burst damage unless if she is played as Nuker.
* Timbersaw's high pure damage and low-cooldown area-of-effect nukes which are 
Whirling Death, 
Timber Chain, 
Chakram and 
Flamethrower from Aghanim's Shard can also destroy Naga Siren's illusions very fast.
* Timbersaw is a common 
Lotus Orb wielder which allows him to reflect Ensnare back at Naga SIren.
Naga Siren
* Avalanche and Toss combo makes short work of Mirror Image's illusions.
* Tiny's cleave with Tree Grab and area of effect damage with Tree Volley will easily wipe out illusions.
Naga Siren
* Zeus's abilities deal high amounts of burst magical damage, which ignores Naga Siren's high armor.
* Arc Lightning is a good way to destroy Naga Siren's illusions due to it's capabilities to bounce between enemies.
* 
Static Field from Aghanim's Shard can automatically hit everything in a big radius, taking a huge chunk of health out of Naga Siren's illusions, regardless of how much health they have.
Omniknight
* Impetus is not blocked by Guardian Angel. A {U:Satyr Banisher} can also be controlled to dispel Guardian Angel.
Additional:
* Enchantress's 
Impetus deals pure damage instead of physical damage and ignores Guardian Angel, thus fully negating one of Omniknight's most important abilities for teamfights.
* Similar to Doom, Enchantress can use 
Enchant on Satyr Banisher, which will give her access to Satyr Banisher's 
Purge, and allow her to remove Heavenly Grace and Guardian Angel.
Omniknight
* 
Doom applies a basic dispel upon cast, so it can remove Guardian Angel.
* Casting Doom on Omniknight will also prevent him from healing allies with Purification, or casting buffs like Repel and Guardian Angel, basically turning him into a harmless creep.
Additional:
* Doom turns Omniknight into a walking creep, or completely takes out his buffed cores, also removing Heavenly Grace and Guardian Angel in the process.
* With 
Devour used on Satyr Banisher, Doom will have access to Satyr Banisher's Purge, which will allow him to remove Heavenly Grace and Guardian Angel.
Omniknight
* Jingu Mastery will still add stacks even through Guardian Angel.
* Monkey King can join a fight whenever he chooses to, meaning he can simply go directly onto Omniknight.
* During the laning phase, Jingu Mastery with Boundless Strike will kill off Omniknight, while Purification is weak.
* Heavenly Grace is useless against Monkey King's ultimate and Jingu Mastery bonuses.
Naga Siren
* 
Waveform clear Mirror Image illusions from Naga Siren. And though Ensnare can prevent Morphling from using Waveform to escape, he can easily dispel it with Manta Style, a common item on Morphling.
* 
Morph allows Morphling to copy Naga Siren's abilities and combine them with Manta Style, a commong item for Morphling, to destroy Naga Siren's illusions. Aghanim's Scepter upgraded Morph also allows Morphling to create a strong illusion of Naga Siren that can do the same and which can also allow Morphling to close the gap on Naga Siren.
Naga Siren
* Many stacks of Sticky Napalm, combined with Flamebreak and Firefly, allows Batrider to destroy illusions from Mirror Image.
* If Batrider can manage to destroy all illusions from Naga Siren, he will be able to use Flaming Lasso on the real one, and will be able to drag her toward his team, potentially preventing Naga Siren from escaping with Song of the Siren.
Additional:
* Many stacks of Sticky Napalm, combined with Flamebreak and Firefly, allows Batrider to destroy illusions from Mirror Image.
* If Batrider can manage to destroy all illusions from Naga Siren, he will be able to use Flaming Lasso on the real one, and will be able to drag her toward his team, potentially preventing Naga Siren from escaping with Song of the Siren.
Naga Siren
* Heroes with AoE nukes will clear her illusions in no time, especially if they are percentage-damage-based, like Underlord's Firestorm, Elder Titan's Earth Splitter, Enigma's Midnight Pulse, Zeus's Arc Lightning, Jakiro's Liquid Frost from Aghanim's Shard etc.
Omniknight
* Although Sven relies often on physical damage, an Aghanim's Scepter upgraded 
Storm Hammer can dispel Guardian Angel with its wide radius.
Naga Siren
* Heroes whose attacks can affect multiple enemies at once will clear Naga Siren's illusions. Such heroes include 
Sven, Magnus, Dragon Knight, Luna, Medusa, 
Templar Assassin, Gyrocopter, Muerta.
Omniknight
* Purification can heal allies while dealing pure damage to Sven.
* Heavenly Grace can remove Storm Hammer's debuff immediately or make it a very mediocre stun.
* Guardian Angel negates Sven's massive damage during God's Strength.
* It should also be noted Sven can remove Omniknight's active spells with Aghanim's Scepter.
Naga Siren
* Heroes that rely on illusions typically spawn very strong illusions inside Dark Seer Wall of Replica that he can use against them or their team: Phantom Lancer, Chaos Knight, Naga Siren, Terrorblade.
Omniknight
* Heroes with large magical AoE damage will fare well against Omniknight: 
Lich, Ancient Apparition, Jakiro, 
Disruptor.
Naga Siren
* Since Naga Siren is a hero who barely goes for Black King Bar, she is vulnerable to nukers with strong magical damage and big area-of-effect spells in every game more than any other carry heroes: Sand King, Jakiro, 
Leshrac, Lina, Earthshaker, Zeus.
Omniknight
* Heroes who can harass Omniknight out of lane will keep him weak in the mid game: 
Viper, Venomancer, 
Clinkz.
Naga Siren
* Heroes who are reliant on illusions: Chaos Knight, Phantom Lancer, Naga Siren.
Additional:
* Centaur's 
Retaliate will harm all attacking enemies, which will allow Centaur Warrunner to see which is the real Naga Siren.
* A well timed 
Hoof Stomp followed by 
Double Edge will clear all Naga's illusions and prevent Naga Siren from escaping with Song of the Siren.
Naga Siren
* Naga Siren's Song of the Siren may be useful but Poof will destroy all of her illusions.
Omniknight
* Heroes that can purge buffs can dispel Guardian Angel: 
Invoker, Shadow Demon, Oracle.
Additional:
* Demonic Purge can dispel Guardian Angel on the key target during combat, allow your allies to finish them.
Naga Siren
* As long as Windranger is able to identify the real hero among the illusions, heroes relying on them can be easily tagged with Focus Fire: Chaos Knight, Terrorblade, Phantom Lancer, Naga Siren.
Omniknight
* Heroes that rely on slows or low-duration stuns have trouble catching Weaver: Omniknight, Lich.
Omniknight
* Heroes with large magical AoE damage will fare well against Omniknight: Lich, Ancient Apparition, Jakiro, Disruptor.
Naga Siren
* 
Keeper of the Light can stall pushes with 
Illuminate. This makes him strong against pushing heroes: Terrorblade Naga siren Nature's Prophet and Anti-Mage
Omniknight
* Heroes who can drain mana can make Omniknight useless after he uses one or two abilities: Lion, Anti-Mage, Nyx Assassin.
Omniknight
* Heroes with naturally low mana can be easily shut down by E.M.P.: Sven, 
Tiny, Wraith King, Omniknight
Additional:
* 
Tornado dispels Heavenly Grace and Guardian Angel from multiple targets.
* Guardian Angel is generally useless against Invoker as he primarily relies on magical damage.
* 
E.M.P. depletes Omniknight's already small mana pool.
* Invoker's many disables keep Omniknight's team occupied until Guardian Angel times out.
Naga Siren
* Heroes who are reliant on illusions or summons: Chaos Knight, Broodmother, Naga Siren.
Omniknight
* Heroes who can harass Omniknight out of lane will keep him weak in the mid game: Viper, Venomancer, Clinkz.
Omniknight
* Heroes with large physical resistance do not counter Muerta's 
Pierce the Veil such as Omniknight or 
Tidehunter.
Naga Siren
* Heroes whose attacks can affect multiple enemies at once will clear Naga Siren's illusions. Such heroes include Sven, Magnus, Dragon Knight, Luna, Medusa, Templar Assassin, Gyrocopter, Muerta.
Naga Siren
* Any long duration disables that can pierce through both, Pierce The Veil and Black King Bar are devastating against Muerta: Enigma's Black Hole, Dawnbreaker's Solar Guardian, Axe's Berserker's Call, Naga Siren's Aghanim's Scepter upgraded Ensnare and Reel In from Aghanim's Scepter, Jakiro's Aghanim's Scepter upgraded Macropyre, 
Bane's 
Fiend's Grip, 
Pudge's 
Dismember, Batrider's Flaming Lasso, 
Beastmaster's 
Primal Roar, Grimstroke's Soulbind, Medusa's Stone Gaze, Magnus's Reverse Polarity.
Naga Siren
* Medusa's 
Split Shot and 
Mystic Snake combined with 
Mjollnir, a common item for Medusa, will whittle down all of Naga Siren's illusions, including Naga Siren herself.
* Medusa's Stone Gaze can disable Naga Siren even for the duration of Song of the Siren and even if Naga Siren is spell immune, discouraging Naga Siren from even trying to use Song of the Siren to save herself or counter-initiate against Medusa.
Additional:
* Medusa's Split Shot and Mystic Snake combined with Mjollnir, a common item for Medusa, will whittle down all of Naga Siren's illusions, including Naga Siren herself.
* Medusa's Stone Gaze can disable Naga Siren even for the duration of Song of the Siren and even if Naga Siren is spell immune, discouraging Naga Siren from even trying to use Song of the Siren to save herself or counter-initiate against Medusa.
Naga Siren
* Heroes that build 
Diffusal Blade or can fit it well into their item build will also make Medusa much less tanky: 
Riki, Naga Siren, Terrorblade, 
Juggernaut, Spectre, 
Slark.
Omniknight
* Being mostly a physical damage dealer, Sniper's effectiveness is greatly reduced by Omniknight's Guardian Angel.
* Omniknight's 
Degen Aura allows him to slow sniper and catch him. Sniper has to then use some escape item.
* Omniknight can also protect an ally from being finished off by Assassinate by using Purification and Repel which grants a massive strength boost.
Naga Siren
* Ensnare with her attacks allows Naga Siren to gank Sniper easily.
* Rip Tide removes Sniper's very little armor.
Omniknight
* Guardian Angel completely negates all of Lycan's damage since Lycan mainly deals physical damage.
* Purification can also be a problem for Lycan, as Purification deals damage around the target, which poses a problem for him and his summons.
Naga Siren
* Lycan is a hero focused entirely on single target physical damage and lacks disables or AoE damage. Due to this, he will have difficulties dealing with illusions or Naga Siren's Ensnare.
Omniknight
* Purification heals a teammate targeted by Reality Rift and heavily damages Chaos Knight and his illusions in the process.
* Guardian Angel blocks all of Chaos Knight's damage for a long duration.
Additional:
* 
Phantasms can be easily killed with Purification.
* Heavenly Grace dispels the stun from 
Chaos Bolt and the armor reduction from 
Reality Rift.
* Guardian Angel works well against Chaos Knight's overwhelming reliance on physical burst damage.
Naga Siren
* Illusion-based and multi-unit heroes can take advantage of Chaos Knight's lack of area damage: Naga Siren, Phantom Lancer, Broodmother
Omniknight
* Guardian Angel can negate all the physical damage output during Chronosphere.
* When Faceless Void Time Walk's on top of an enemy it becomes a perfect target for Purification
Additional:
* Guardian Angel can negate all the physical damage output from Faceless Void during 
Chronosphere.
* If Faceless Void 
Time Walks on top of an ally Purification + Heavenly Grace can turn the fight around.
Naga Siren
* Ensnare prevents using any kind of movement abiilties, Making Naga Siren good against heroes who rely on gap-closing abilities to escape: 
Phantom Assassin, Magnus, Slark, Riki, 
Faceless Void, 
Storm Spirit.
Omniknight
* Slark's dependence on Pounce and close range makes him very easy to hit with Purification and 
Hammer of Purity.
* Slark's damage, even with a high count of Essence Shift stacks, is easily negated by Omniknight's heals and Guardian Angel.
Naga Siren
* Ensnare prevents using any kind of movement abiilties, Making Naga Siren good against heroes who rely on gap-closing abilities to escape: Phantom Assassin, Magnus, Slark, Riki, Faceless Void, Storm Spirit.
Omniknight
* Riki takes a lot of damage from Purification while ganking Omniknight's allies or himself.
* Heavenly Grace instantly purges the slow from Diffusal Blade, while also providing a large amount of survivability for his victim.
* Degen Aura can hinder Riki's positioning tactics and put a heavy toll on Riki's already poor movement speed.
* Omniknight can easily save his allies by using Guardian Angel in combat.
Naga Siren
* Ensnare prevents using any kind of movement abiilties, Making Naga Siren good against heroes who rely on gap-closing abilities to escape: Phantom Assassin, Magnus, Slark, Riki, Faceless Void, Storm Spirit.
Omniknight
* Purification and Hammer of Purity can easily catch Phantom Assassin once she jumps with 
Phantom Strike in to attack.
* Heavenly Grace can be used to dispel slow from 
Stifling Dagger, and disables from the items Phantom Assassin relies on.
* Phantom Assassin depends entirely on physical attacks and her damage output is 100% physical. Therefore, since she has no any sources of magical damage output and hates going for items that deal magical damage like 
Dagon, 
Ethereal Blade and 
Revenant's Brooch, Guardian Angel will render her completely useless.
* Purification, Heavenly Grace and Guardian Angel can be used to save an allied hero before Phantom Assassin can finish them off with 
Coup De Grace.
Additional:
* Purification and Hammer of Purity can easily catch Phantom Assassin once she jumps with Phantom Strike in to attack.
* Heavenly Grace can be used to dispel slow from Stifling Dagger, and disables from the items Phantom Assassin relies on.
* Phantom Assassin depends entirely on physical attacks and her damage output is 100% physical. Therefore, since she has no any sources of magical damage output and hates going for items that deal magical damage like Dagon, Ethereal Blade and Revenant's Brooch, Guardian Angel will render her completely useless.
* Purification, Heavenly Grace and Guardian Angel can be used to save an allied hero before Phantom Assassin can finish them off with Coup De Grace.
Naga Siren
* Ensnare prevents using any kind of movement abiilties, Making Naga Siren good against heroes who rely on gap-closing abilities to escape: Phantom Assassin, Magnus, Slark, Riki, Faceless Void, Storm Spirit.
Naga Siren
* Heroes who rely on illusions will see them destroyed easily by Overwhelming Odds: Phantom Lancer, Chaos Knight, Terrorblade, Naga Siren
Omniknight
* Purification prevents Legion Commander from killing her target, and will always hit her during Duels.
* Guardian Angel completely wastes Duel's duration and can save an ally across the map when upgraded with Aghanim's Scepter.
Additional:
* Both Guardian Angel and Purification are perfect counters against 
Duel.
Naga Siren
* Song of the Siren lasts long enough to prevent a successful Duel (but only if Naga wasn't the target).
Omniknight
* Heroes who possess abilities that can save targets from being killed by Reaper's Scythe: 
Abaddon, Bane, 
Outworld Destroyer, Shadow Demon, Omniknight, etc.
Naga Siren
* Illusions make it difficult for Necrophos to target his Reaper's Scythe correctly, thus giving illusion heroes like Chaos Knight or Naga Siren an edge against Necrophos.
Omniknight
* Heroes with strong dispels can dispel Bane's disables from their allies: Oracle, 
Legion Commander, Omniknight.
Naga Siren
* Heroes with illusions and summons can swarm and overwhelm Bane, who has no area abilities to deal with them outside from Aghanim's Shard upgraded 
Brain Sap: Broodmother, Chaos Knight, Naga Siren, Nature's Prophet, Phantom Lancer, Terrorblade, Visage, 
Warlock, Wraith King.
Omniknight
* Omniknight with Heavenly Grace
* Heroes that can remove the Track debuff with their skills:
* Abaddon with 
Aphotic Shield and 
Borrowed Time
* 
Huskar with 
Life Break
* Juggernaut with 
Blade Fury
* Legion Commander with 
Press the Attack
* 
Lifestealer with 
Rage and 
Infest
* Naga Siren with Mirror Image
* Omniknight with Heavenly Grace
* Oracle with Fortune's End and 
False Promise
* Phantom Lancer with 
Doppelganger
* Slark with 
Dark Pact
* 
Ursa with 
Enrage
* 
Weaver with 
Time Lapse
* Tidehunter with 
Kraken Shell when damage received reaches the threshold.
Naga Siren
* Naga Siren with Mirror Image
* Heroes that can remove the Track debuff with their skills:
* Abaddon with Aphotic Shield and Borrowed Time
* Huskar with Life Break
* Juggernaut with Blade Fury
* Legion Commander with Press the Attack
* Lifestealer with Rage and Infest
* Naga Siren with Mirror Image
* Omniknight with Heavenly Grace
* Oracle with Fortune's End and False Promise
* Phantom Lancer with Doppelganger
* Slark with Dark Pact
* Ursa with Enrage
* Weaver with Time Lapse
* Tidehunter with Kraken Shell when damage received reaches the threshold.
Additional:
* Bounty Hunter is a single target damage dealer, so he will not fare well against Naga Siren. Even though Bounty Hunter can use 
Track on her, Mirror Image will dispel the effect. Ensnare also reveals invisible units while they're rooted, putting Bounty Hunter at a disadvantage.
Naga Siren
* Naga Siren can make landing Chen's combo very hard due to her being an illusion hero thanks to Mirror Image.
* Rip Tide can deal big damage to Chen and reduce Chen's armor, as well as easily kill all of Chen's creeps.
* Naga Siren often builds 
Radiance, which allows her to quickly clear Chen's creeps.
* Ensnare will prevent Chen from escaping.
* With Aghanim's Scepter, Naga Siren can get access to Reel In, which can separate Chen from his creeps and draw him closer to Naga Siren and her team to finish her off. To make things worse, Chen has no way to cancel Reel In on his own, and must rely on outside from {U:Centaur Conqueror} or {U:Mud Golem} under his control.
* Carry or Nuker Naga Siren can often finish off Support Chen before he can have a chance to activate 
Hand of God.
Additional:
* Naga Siren can make landing Chen's combo very hard due to her being an illusion hero.
* Rip Tide can deal big damage to Chen and reduce Chen's armor, as well as easily kill all of Chen's creeps.
* Naga Siren often builds Radiance, which allows her to quickly clear Chen's creeps.
* Ensnare will prevent Chen from escaping.
* With Aghanim's Scepter, Naga Siren can get access to Reel In, which can separate Chen from his creeps and draw him closer to Naga Siren and her team to finish her off. To make things worse, Chen has no way to cancel Reel In on his own, and must rely on outside from {U:Centaur Conqueror} or {U:Mud Golem} under his control.
* Carry or Nuker Naga Siren can often finish off Support Chen before he can have a chance to activate Hand of God.
Naga Siren
* Naga Siren can very easily dispel the 
Reflection with Mirror Image. And Besides Reflection that can be used to detect real Naga Siren, Terrorblade has no other ways to deal with Naga Siren's illusions. And what's worse is that Naga Siren can much easily detect the real Terrorblade due to 
Conjure Image having illusions having different colors. In addition, Terroblade is not a common 
Battle Fury nor Mjollnir wielder to counter this problem.
* Aghanim's Scepter upgraded Ensnare will allow Naga Siren to root Terrorblade even ithrough Black King Bar. And with Aghanim's Scepter, Naga Siren can get access to 
Reel In ability, which can allow her to pull Terrorblade toward herself and her team and away from his illusions, even through Black King Bar.
* Naga Siren can rapidly damage Terrorrblade and weaken Terrorblade's armor with Rip Tide, which combined with Terrorblade's low health and strength gain can almost completely discourage Terrorblade from even being present in teamfights. Rip Tide can also weaken armor of Terrorblade's illusions and damage them.
* Song of the Siren can be used to save an ally whom Terrorblade has used 
Sunder under the condition Naga Siren is quick enough to do it. And since Terrorblade has no "real" burst damage potential outside from Sunder, Naga Siren will usually have plenty of time to save an allied hero on which Sunder was used. Aghanim's Shard upgraded Song of the Siren can also heal her allies around her for it's duration, which allows Naga Siren to nullify effects of Sunder.
* However, Naga Siren's lack of burst damage can make it difficult for her to burst down Terrorblade before he can use Sunder unless Naga Siren has either Black King Bar or 
Linken's Sphere to protect herself against it or if she is played as Nuker.
Additional:
* Naga Siren can very easily dispel the Reflection with Mirror Image. And Besides Reflection that can be used to detect real Naga Siren, Terrorblade has no other ways to deal with Naga Siren's illusions. And what's worse is that Naga Siren can much easily detect the real Terrorblade due to Conjure Image having illusions having different colors. In addition, Terroblade is not a common Battle Fury nor Mjollnir wielder to counter this problem.
* Aghanim's Scepter upgraded Ensnare will allow Naga Siren to root Terrorblade even through Black King Bar. And with Aghanim's Scepter, Naga Siren can get access to Reel In ability, which can allow her to pull Terrorblade toward herself and her team and away from his illusions, even through Black King Bar.
* Naga Siren can rapidly damage Terrorrblade and weaken Terrorblade's armor with Rip Tide, which combined with Terrorblade's low health and strength gain can almost completely discourage Terrorblade from even being present in teamfights. Rip Tide can also weaken armor of Terrorblade's illusions and damage them.
* Song of the Siren can be used to save an ally whom Terrorblade has used Sunder under the condition Naga Siren is quick enough to do it. And since Terrorblade has no "real" burst damage potential outside from Sunder, Naga Siren will usually have plenty of time to save an allied hero on which Sunder was used. Aghanim's Shard upgraded Song of the Siren can also heal her allies around her for it's duration, which allows Naga Siren to nullify effects of Sunder.
* However, Naga Siren's lack of burst damage can make it difficult for her to burst down Terrorblade before he can use Sunder unless Naga Siren has either Black King Bar or Linken's Sphere to protect herself against it or if she is played as Nuker.
Naga Siren
* Naga Siren is a natural split-pusher. With Rip Tide, she will easily out-push Nature's Prophet, farming his treants in the process.
* Ensnare prevents 
Teleportation. Even if he hides inside 
Sprout, Song of the Siren lasts long enough to prevent him from escaping.
Additional:
* Naga Siren is a natural split-pusher. With a Radiance equipped, she will easily keep the lanes pushed out, therefore keeping backdoor protection enabled and preventing Nature's Prophet from dealing building damage.
* Ensnare can prevent Teleportation. Aghanim's Scepter upgraded Ensnare can also affect Nature's Prophet even if he is spell immune. And Reel In from Aghanim's Scepter can also be used to separate Nature's Prophet from his treant and bring him close to Naga Siren and her team to burst him down.
* Song of the Siren will stop Nature's Prophet from escaping even if he has hidden inside of Sprout. Aghanim's Shard upgraded Song of the Siren can also heal her allies and save them from Nature's Prophet.
Omniknight
* Global Guardian Angel will protect his allies from Spectre's 
Haunt, both when they are alone and in teamfights.
* Purification is a major problem for melee enemies, Spectre included, since they must be next to an enemy in order to attack. The AoE damage also allows Spectre to be singled out from her illusions.
* Degen Aura will prevent Spectre from chasing Omniknight, further exacerbated by her terrible mobility outside Haunt.
Naga Siren
* Mirror Image can dispel Frostbite. A similar effect can be achieved with Manta Style, a core item on Naga Siren.
* Song of the Siren can stop Freezing Field regardless of any kind of invisibility as well as allow Naga Siren's team to quickly close the gap on Crystal Maiden.
* With Aghanim's Scepter, Naga Siren can get access to Reel In ability, which can allow her to pull Crystal Maiden toward herself and her team and cancel Freezing Field even through Black King Bar.
Additional:
* Mirror Image can dispel Frostbite.
* Song of the Siren can stop Freezing Field regardless of any kind of invisibility as well as allow Naga Siren's team to quickly close the gap on Crystal Maiden.
* Ensnare allows Naga Siren and her team to quickly catch up with Crystal Maiden and kill her.
* With Aghanim's Scepter, Naga Siren can get access to Reel In ability , which can allow her to pull Crystal Maiden toward herself and her team and cancel Freezing Field even through Black King Bar.
Naga Siren
* Mirror Image can cause Huskar to Life Break the wrong target.
* Rip Tide reduces Huskar's already low armor.
* Song of the Siren allows teams to recover from Huskar's initiation, as well as the damage over time from Burning Spears.
Omniknight
* Repel can be used to dispel 
Gust on the allies affected by it.
* In team fights, Guardian Angel renders Drow Ranger's physical damage useless, and Drow Ranger has no way to purge it. And to make thing worse, Drow Ranger is not a common 
Nullifier wielder to counter this problem at all.
Naga Siren
* Heroes with long-lasting, undispellable debuffs will pinpoint the true Naga Siren: 
Spirit Breaker, Bloodseeker, Witch Doctor.
Omniknight
* In the early game, Omniknight can look like an easy target for Spirit Breaker, but with Purification and Hammer of Purity, what could be an opportunity could quickly turn into disaster.
* Repel can be used to counter Charge of Darkness by minimizing the damage and lowering the stun duration with status resistance.
* Spirit Breaker's Greater Bash from all sources (Charge of Darkness or normal attacks) will deal no damage at all if Omniknight and his allies are protected with presence.
* Due to this, Spirit Breaker's damage will always be lower when targeting Omniknight.
Naga Siren
* Heroes with summons and illusions as Spirit Breaker has no strong AoE capabilities to deal with them: Chaos Knight, Phantom Lancer, Terrorblade, Naga Siren, Broodmother, Warlock, Visage, Nature's Prophet, Shadow Shaman, Lycan, Wraith King.
Omniknight
* Heroes with large magical AoE damage will fare well against Omniknight: Lich, Ancient Apparition, Jakiro, Disruptor.
Omniknight
* Purification allows Omniknight to keep a hero trapped in the Static Storm alive.
* Repel is a reliable source of immunity to the effects of Static Storm.
Naga Siren
* Naga Siren with Mirror Image
* Heroes that can dodge Glimpse:
* Puck with 
Phase Shift
* Riki with 
Tricks of the Trade
* Phantom Lancer with Doppelganger
* Ember Spirit with Sleight of Fist and 
Activate Fire Remnant
* Chaos Knight with Phantasm
* Naga Siren with Mirror Image
* 
Tusk with 
Snowball
* Juggernaut with 
Omnislash
* 
Brewmaster with 
Primal Split
* Lifestealer with Infest
* 
Phoenix with 
Supernova
Omniknight
* Guardian Angel nullifies the physical damage from Exorcism during teamfights. And when upgraded with Aghanim's Scepter, it also prevents Death Prophet from pushing towers. However, Death Prophet can partially counter this issue with Eul's Scepter of Divinity, a common item on Death Prophet.
* Heavenly Grace dispels Silence.
Additional:
* Exorcism's damage is blocked by Guardian Angel.
* Heavenly Grace can dispel Silence allies if Omniknight is able to cast it.
Naga Siren
* Ensnare and Song of the Siren can be used to cancel both, 
Tether and 
Relocate and to close the distance on Io.
* Rip Tide combined with illusions from Mirror Image often finish off Io before he can save himself with Tether or Relocate.
* 
Spirits's weak area-of-effect makes it a bad tool to deal with Naga Siren's illusions from Mirror Image.
* Once Naga Siren buys Aghanim's Scepter, she can gain access to Reel In, which not only allows her to cancel both, Tether and Relocate, but also to pull Io to herself and her team while he is affected with Ensnare, similarly to Batrider's Flaming Lasso.
* Aghanim's Shard upgraded Song of the Siren can also heal the hero Io and his Tethered targed try to gank.
Additional:
* Ensnare and Song of the Siren can be used to cancel both, Tether and Relocate and to close the distance on Io.
* Rip Tide combined with illusions from Mirror Image often finish off Io before he can save himself.
* Spirit's weak area-of-effect makes it a bad tool to deal with Naga Siren's illusions from Mirror Image.
* Once Naga Siren buys Aghanim's Scepter, she can gain access to Reel In, which not only allows her to cancel both, Tether and Relocate, but also to pull Io to herself and her team while he is affected with Ensnare, similarly to Batrider's Flaming Lasso.
* Aghanim's Shard upgraded Song of the Siren can also heal the hero Io and his tethered targed try to gank.
Omniknight
* Heavenly Grace reduces Fireblast stun time and dispels Ignite.
* Purification can heal damaged heroes if needed.
Omniknight
* Guardian Angel makes allies immune to all physical damage, effectively causing Tidebringer to do no damage.
* Purification is a powerful, pure damaging heal that can save Omniknight's allies after Kunkka's large damage.
Naga Siren
* Unless Lone Druid purchases a Black King Bar for his Spirit Bear, Ensnare will easily kite the Spirit Bear.
* Song of the Siren allows Naga Siren and her team to completely bypass the Spirit Bear and hunt for the Lone Druid himself when starting a fight.
* Lone Druid's lack of innate AoE capabilities mean that Naga Siren's illusions have no problem against him.
Omniknight
* Guardian Angel completely counters Winter's Curse if Omniknight is able to cast it.
Additional:
* Guardian Angel completely counters Winter's Curse, allowing his team to survive Winter Wyvern's initiation.
* Purification and Repel are very useful against Arctic Burn, Splinter Blast and Winter's Curse as well.
Naga Siren
* Naga Siren's illusions from Mirror Image can depush the lanes pushed by the Tempest Double, relieving the pressure.
* Mirror Image can dispel Flux, and the illusions can stop Flux from working to it's full power.
Additional:
* Song of the Siren stops Arc Warden from acting and allows Naga Siren's team to close in on him, past his 
Magnetic Field.
* Mirror Image dispels 
Flux. The illusions created from it also disable the slow from Flux if Arc Warden casts it after Mirror Image.
* Arc Warden's playstyle heavily favors split-pushing, which Naga Siren can compete against with her illusions.
Naga Siren
* Song of the Siren completely wastes Abaddon Borrowed Time while keeping him in place.
* Naga Siren is able to simply dispel Abaddon's 
Curse of Avernus with Mirror Image before getting hit 4 times consecutively.
* Although Naga Siren's illusions can be easily destroyed by Aphotic Shield, Naga Siren can resolve that issue easily by purchasing 
Heart of Tarrasque to drastically increase her durability. Plus, the said item makes Naga Siren harder to be distinguished from her illusions.
Naga Siren
* Heroes with summons like Broodmother, Enigma, Nature's Prophet; or illusions, like Naga Siren, Terrorblade are effective at keeping the choke points and rune spawns safe from Proximity Mines.
Omniknight
* Heroes that can save their allies can be a big problem for Mars: 
Dazzle, Omniknight.
Naga Siren
* Heroes whose attacks can affect multiple enemies at once will clear Naga Siren's illusions. Such heroes include Sven, Magnus, Dragon Knight, Luna, Medusa, Templar Assassin, Gyrocopter, Muerta.
Omniknight
* Any hero who can counter-initiate in anticipation without getting caught in Reverse Polarity: Sven, Omniknight, Enigma, Luna, Naga Siren, Mars, Jakiro, Venomancer, Elder Titan, Faceless Void, 
Rubick, Keeper of the Light, 
Pugna, Invoker, Spectre, Alchemist, 
Treant Protector, Lina, Oracle, Zeus, Shadow Shaman, Phoenix, Razor, Huskar, Batrider, 
Kunkka, Tidehunter, Wraith King, Sand King, Medusa, Dawnbreaker.
Naga Siren
* Any hero who can counter-initiate in anticipation without getting caught in Reverse Polarity: Sven, Omniknight, Enigma, Luna, Naga Siren, Mars, Jakiro, Venomancer, Elder Titan, Faceless Void, Rubick, Keeper of the Light, Pugna, Invoker, Spectre, Alchemist, Treant Protector, Lina, Oracle, Zeus, Shadow Shaman, Phoenix, Razor, Huskar, Batrider, Kunkka, Tidehunter, Wraith King, Sand King, Medusa, Dawnbreaker.
Omniknight
* Heroes with spell immunity or pseudo-blinks which provide invulnerability: Lifestealer, Juggernaut, Omniknight, Huskar, and Tusk have spells which allow them to easily escape Dream Coil.
Naga Siren
* Illusion heroes like the aforementioned Phantom Lancer or Naga Siren, or heroes that tend to buy Manta Style, like Luna or Juggernaut, will give Slardar a hard time, as his damage is single-targeted.
Naga Siren
* Ensnare prevents using any kind of movement abiilties, Making Naga Siren good against heroes who rely on gap-closing abilities to escape: Phantom Assassin, Magnus, Slark, Riki, Faceless Void, Storm Spirit.
Omniknight
* Heroes who rely strongly on melee physical damage will fare badly against Omniknight's Guardian Angel: Phantom Assassin, Juggernaut, Dragon Knight, Lycan, Ursa, 
Troll Warlord
Naga Siren
* Blade Fury offers good AoE damage to clear illusions and can hurt the real Naga Siren as well if she chooses to blend in the illusions. Diffusal Blade does nothing to Juggernaut either when he uses Blade Fury.
* Aghanim's Shard upgraded Blade Fury along with Lv 20 DPS talent will shred all illusions almost instantly, especially when combined with Mjollnir, a common item for Juggernaut.
Omniknight
* Guardian Angel completely negates all physical damage, including Omnislash.
Additional:
* Omnislash (and 
Swiftslash) is blocked by Guardian Angel.
Naga Siren
* Illusion-based heroes are effective against Omnislash and Juggernaut's single-targeted damage: Naga Siren, Chaos Knight, Terrorblade,Phantom Lancer.
Naga Siren
* Heroes with illusions: Chaos Knight, Naga Siren, Phantom Lancer, Terrorblade
Omniknight
* Omniknight can dispel Hex or Shackles with Heavenly Grace. He can also heal teammates who you disabled. The same goes for Abaddon's Aphotic Shield.
Naga Siren
* Heroes with summons and illusions such as Broodmother and Naga Siren, are ill-suited for Wraith King to fight, as he has no source of waveclear.
Omniknight
* Heroes who rely strongly on melee physical damage will fare badly against Omniknight's Guardian Angel: Phantom Assassin, Juggernaut, Dragon Knight, Lycan, Ursa, Troll Warlord
Naga Siren
* Illusion heroes, such as Naga Siren, Phantom Lancer, Chaos Knight, Terrorblade will become strong against Tinker in the late game. Without Aghanim's Scepter Tinker is forced to defensively disarm heroes with Laser, leaving illusions free to deal physical damage which Tinker's low armor makes highly effective. In addition, Mjollnir or Battle Fury, two common pickups against illusion heroes, don't work well on Tinker at all.
Naga Siren
* Heroes whose attacks can affect multiple enemies at once will clear Naga Siren's illusions. Such heroes include Sven, Magnus, Dragon Knight, Luna, Medusa, Templar Assassin, Gyrocopter, Muerta.
Naga Siren
* Ensnare disables Templar Assassin's invisibility and Blink Dagger (a core item on Templar Assassin), and her illusions will break 
Refraction easily.
Naga Siren
* Sand King and Phoenix have many tools to deal with multiple enemies at once, which will work well against a crowd of illusions.
Naga Siren
* Song of the Siren does not affect Supernova, which allows her and her team to focus the egg while the enemy team is affected by sleep.
* Phoenix cannot use 
Icarus Dive for escaping when rooted by Ensnare.
* However, Phoenix has many area-of-effect abilities that allow him to clear Naga Siren's illusions from Mirror Image.
Naga Siren
* Heroes with long-lasting, undispellable debuffs will pinpoint the true Naga Siren: Spirit Breaker, Bloodseeker, Witch Doctor.
Omniknight
* Guardian Angel protects allies from Death Ward's physical damage.
* Purification and Heavenly Grace will most likely save teammates from dying to Maledict.
Omniknight
* Heroes who can harass Omniknight out of lane will keep him weak in the mid game: Viper, Venomancer, Clinkz.
Naga Siren
* Naga Siren can easily disjoint, and dispel 
Corrosive Skin with Mirror Image.
* Since Viper is mostly a single-target hero, he will not have almost any chance against Naga Siren because she is an illusion based hero.
* Viper has no burst damage, so Naga Siren will have plenty of time to use Aghanim's Shard upgraded Song of the Siren heal her allies before Viper can finish them off.
Naga Siren
* Heroes with long cast animations can be continuously interrupted by Battery Assault: 
Centaur Warrunner, Jakiro, Leshrac, Naga Siren, Underlord.
Omniknight
* Purification does great damage to Clockwerk when fighting an enemy inside Power Cogs.
* Due to Clockwerk's very low damage output, Omniknight will have more than enough time to Purification and Heavenly Grace any enemy hero Clockwerk initiates on.
* For the same reasons, Omniknight also makes a powerful ally for Clockwerk when the situation is reversed.
Naga Siren
* Heroes with long-lasting, undispellable debuffs will pinpoint the true Naga Siren: Spirit Breaker, Bloodseeker, Witch Doctor.
Omniknight
* Guardian Angel's near invulnerability denies Bloodseeker the bonuses from Thirst, preventing him from gaining the upper hand in teamfights.
* Purification's pure damage makes it hard for Bloodseeker to pursue enemies, and prevents him from replenishing his health by finishing off enemies.
Naga Siren
* Heroes that heavily depend on illusions or summons, (Naga Siren, Terrorblade, Phantom Lancer, Lycan,...) are vulnerable to Sleight of Fist and even more so if Ember Spirit has Battle Fury.
Omniknight
* The pure damage provided by Purification is a great addition for killing Ember Spirit, as well as a good way of saving teammates.
* Guardian Angel will temporarily save his allies from Sleight of Fist's physical damage, and Ember Spirit is not a hero that will get 
Orchid Malevolence to counter it.
Omniknight
* Heroes that have a weak laning stage: Spectre, Nyx Assassin, 
Clockwerk, Spirit Breaker, Omniknight, Pudge.
Naga Siren
* Mirror Image can be effective since Night Stalker cannot withstand fighting illusions. If he's unable to tell which Naga Siren is real, he will have a hard time landing his 
Void. However, if Night Stalker obtains an Aghanim's Scepter, the upgraded Void will hit and may even locate the real Naga Siren in fights.
Additional:
* Ensnare and Song of the Siren prevents Night Stalker from escaping and ganking during daytime or even nighttime.
* Rip Tide reduces Night Stalker's armor, making him easier to focus down.
* Mirror Image can be effective against Night Stalker, due to his single target abilities.
Naga Siren
* Heroes who are illusion based, or even heroes who frequently build Manta Style can be cleared quickly by Pangolier's high damage, or lose their damage ouput because of Lucky Shot: Chaos Knight, Naga Siren
Naga Siren
* Heroes with powerful rooting abilities will disable most of Pangolier's skills, a bonus point if it pierces spell immunity since it will also be able to stop Pangolier during his Rolling Thunder: Treant Protector, Meepo, Crystal Maiden, Dark Willow, Underlord, Naga Siren
Naga Siren
* 
Flak Cannon and Call Down can easily clear Naga Siren's illusions.
Omniknight
* Guardian Angel negates most of Gyrocopter's physical АоЕ damage.
* Heavenly Grace dispels Homing Missile stun.
Naga Siren
* Heroes whose attacks can affect multiple enemies at once will clear Naga Siren's illusions. Such heroes include Sven, Magnus, Dragon Knight, Luna, Medusa, Templar Assassin, Gyrocopter, Muerta.
Omniknight
* Heroes who rely strongly on melee physical damage will fare badly against Omniknight's Guardian Angel: Phantom Assassin, Juggernaut, Dragon Knight, Lycan, Ursa, Troll Warlord
Naga Siren
* Dazzle can instantly destroy all of Naga Siren's illusions from Mirror Image with Aghanim's Shard upgraded 
Poison Touch used on her or any of her illusions.
Naga Siren
* Mirror Image's illusions can easily walk straight at Dazzle and attack him, due to Dazzle's lack of reliable AoE nukes or disables.
* Ensnare roots Dazzle or his allies, making it harder to stay in range of Dazzle's saving abilities.
* Song of the Siren can be used to initiate a fight with superior positioning, potentially zoning Dazzle's high-impact spells out of the fight.
Omniknight
* All of Omniknight's abilities are valuable for Rubick to 
Spell Steal, and Omniknight has no throwaway ability to cover his last used spell.
Naga Siren
* Song of the Siren is very difficult for Rubick to Spell Steal when he is affected by sleep.
* Ensnare and Rip Tide together with some attacks can take Rubick down quickly, due to his low health pool and armor.
* Naga Siren usually buys Diffusal Blade, which may prevent Rubick from using his abilities.
* Mirror Image allows Naga Siren to dodge the incoming stun from 
Telekinesis (when she is not a target), and it can also dispel 
Fade Bolt's damage reduction debuff.
Omniknight
* Heroes who can drain mana can make Omniknight useless after he uses one or two abilities: Lion, Anti-Mage, Nyx Assassin.
Naga Siren
* Nyx Assassin's skillset is mostly single-targeted, therefore he will have difficulties against heroes with illusions and summons: Naga Siren, Broodmother, Lycan, Visage, Phantom Lancer. And to make things worse, Nyx Asassin is not a common Battle Fury, 
Maelstrom, Mjollnir, Gleipnir or Radiance wielder to counter this problem.
Naga Siren
* Axe will destroy her illusions by proccing 
Counter Helix more often due to him being hit by more attacks.
Omniknight
* Omniknight's healing prevents allies from dropping low enough for 
Culling Blade
* Heavenly Grace dispels 
Battle Hunger.
* Axe also tends to get close to allied heroes in order to damage them with his Counter Helix, which can easily be punished by Purification.
Omniknight
*
Arcane Orb's pure damage penetrates Guardian Angel's defense.
Astral Imprisonment's mana steal is devastating to Omniknight's already low mana pool.
*
Naga Siren
*
Arcane Orb allows Outworld Destroyer's attacks to deal pure damage that can bypass Naga Siren's armor, and which can clear her illusions in no time.
Astral Imprisonment can be used to harass Naga Siren by reducing her maximum mana and to prevent Naga Siren from escaping with Song of the Siren. Outworld Destroyer can also use 
Astral Imprisonment to protect himself from Naga Siren.
Sanity's Eclipse will most likely instantly kill Naga Siren along with her illusions. Even if Naga Siren survives 
Sanity's Eclipse, it's mana allergy debuff will discourage Naga Siren from using her abilities as the mana allergy will heal Outworld Destroyer if she uses them for it's duration.
*
*