* Being a hero with low health and abysmal mobility, Lina can nuke her down easily.
* Since Crystal Maiden's Freezing Field is a channeled ability, Lina can use her Light Strike Array to cancel it easily.

* Dragon Slave deals reliable magic damage during the laning phase against Mars.
* Lina's Eul's Scepter of Divinity and Light Strike Array combo can interrupt Mars from being disruptive for a decent amount of time and leave him vulnerable for follow up stuns.
* Laguna Blade deals massive magical damage, and pure damage with Aghanim's Scepter.

* Snowball allows Tusk to easily cancel Freezing Field from a safe distance without putting himself in any danger.
* Walrus PUNCH! is most certainly a high enough damage nuke to easily kill off Crystal Maiden.
* Ice Shards can prevent the already immobile Crystal Maiden from escaping, making her an easy kill for either Tusk or a teammate.
Additional:
* Crystal Maiden's low health and armor make her an easy target for Walrus PUNCH!
* Tusk's Snowball can protect allies and cancel Freezing Field.
* Snowball and Walrus PUNCH! can interrupt Freezing Field.

* Snowball can protect Tusk and his teammates from a Spear of Mars' stun after an Arena of Blood, and with proper targeting, even bring them out of the Arena. This is especially noticeable in the earlier stages of the game before allies buy Black King Bar and rely on this less. Even during the late-game, Tusk can purchase a Blink Dagger to save allies that are caught before Black King Bars can be used by Blinking in and Snowballing out.
* Tag Team is a constant threat to Mars in-lane, as it deals significant damage and slow, making Bulwark slightly ineffective.
* It is worth noting that Ice Shards can be detrimental to Tusk's own team by creating terrain that Spear of Mars can latch on, though using it conservatively is a good enough solution in most cases.

* Juggernaut and Lifestealer have abilities (Blade Fury and Rage respectively) that prevent Crystal Maiden from using her spells on them in the early game, before Black King Bar and other magical reduction is even an issue.

Additional:
* Crystal Maiden is an ideal target for Lifestealer due to her poor mobility and low health pool. Lifestealer can usually catch up to her simply by casting Rage, as none of her abilities pierce through magic immunity. Freezing Field can potentially make her even more vulnerable to Lifestealer while under Rage as she is even more immobile while channeling it.
* Lifestealer commonly buys Abyssal Blade, which allows him to cancel Freezing Field, even if Crystal Maiden is spell immune.
* Alternatively, Aghanim's Scepter upgraded Infest combined with Abyssal Blade and with items that provide attack speed which Lifestealer commonly buys allow him to to cancel Freezing Field from within the Crystal Maiden.

* Rage, acting as a pseudo-Black King Bar, completely negates Mars' initiation if used in time.
* Feast does damage and heals based on max health, perfect against high-health strength heroes like Mars.
* Infest allows Lifestealer to potentially save allies from Mars' initiation with a quick burst of extra health.

* The slow from Torrent makes Crystal Maiden's already bad movement speed even worse.
* Kunkka has many tools to interrupt Freezing Field (most notably Torrent, Ghostship and Torrent Storm from Aghanim's Scepter), as she is an easy target while channeling it.
* It is worth noting that most of Kunkka's abilities do not pierce through spell immunity, so purchasing a Black King Bar might help Crystal Maiden in this regard.

* Kunkka's Ghostship and Torrent disrupt fights in Arena Of Blood.

* Crystal Maiden will be not able to cast her Freezing Field while being constantly stunned by Enigma's Malefice.
* Enigma's Black Hole can cancel Freezing Field's channeling regardless of her Glimmer Cape and Black King Bar.

* Heroes with high magical or pure damage will bypass Bulwark: Timbersaw, Dark Willow, Enigma, Invoker, Pugna, Skywrath Mage, Tinker, Zeus, Oracle.

* Generally, any fragile heroes will have a hard time dealing with Undying's tankiness, and even more so if Decay is used on them. Some examples are Crystal Maiden and Witch Doctor.

* Decay, Soul Rip and Flesh Golem all deal magical damage which ignores Bulwark.
* Decay reduces Mars' natural strength and therefore his health pool, which is what he relies on to trade effectively in lane.

* Vulnerable spellcasters with no escape mechanisms are easy targets for Huskar: Lich, Crystal Maiden, Silencer, Keeper of the Light, Venomancer, etc.

* Burning Spear's magical damage is very troublesome for Mars in the laning stage.
* Life Break's percentage-based magical damage bypasses Bulwark, and can also be used to jump in or out of Arena Of Blood.

* Heroes who can easily harass Crystal Maiden out of lane in the early game (Clinkz, Viper) can prevent Crystal Maiden from being able to level effectively, and can ultimately slow down her level 6, 12, and 18 to a point where enemy carries already have items to address her ultimate.

* Nethertoxin breaks the damage block from Bulwark.
* Poison Attack and Viper Strike's slows make it difficult for Mars to contribute to fights due to his low mobility.
Additional:
* Viper Strike can disable Bulwark entirely, making Mars far less tanky. Using Nethertoxin inside Arena of Blood may discourage enemies from following up with Mars's initiation.
* Rod of Atos is currently common on Viper and keeps Mars in position long enough to be killed.
* However, Viper is not very tanky earlier in the game, so positioning against Mars is important for Viper since a well-timed Spear of Mars can be the end of Viper.

* Heroes that have small health pools and little to no escape mechanisms are even easier prey for Necrophos. Ghost Shroud's slow will allow him to catch him with them, and get nuked down with his abilities, even preventing retaliation due to Reaper's Scythe's stun. Such heroes include Crystal Maiden, Witch Doctor, Warlock or Shadow Fiend.

* Necrophos' largely magical damage completely ignores Bulwark.
* Ghost Shroud protects Necrophos from God's Rebuke but more importantly stops Mars from being a threat in lane.

* In general, heroes with AoE or long range disables (such as Faceless Void with Chronosphere, Pudge with Meat Hook and Elder Titan with Echo Stomp) hinder Crystal Maiden, preventing her from using Freezing Field to help her team in a fight.

* Time Dilation while Spear of Mars and God's Rebuke are on cooldown will make these abilities unusable for a long time, rendering Mars nearly useless.
* Mars cannot turn inside the Chronosphere, which makes it easy to attack him from the back, bypassing Bulwark completely.
Additional:
* Time Walk allows Faceless Void to escape or enter Arena Of Blood, and helps him recover from Mars' burst damage.
* Time Lock's magical damage ignores Bulwark.
* Chronosphere allows Faceless Void to reposition behind Mars, ignoring his Bulwark while he is helplessly frozen in time.

* Berserker's Call can interrupt Freezing Field, even through Black King Bar and/or Glimmer Cape.
* Battle Hunger makes Crystal Maiden's already bad movement speed even worse.
* Axe frequently builds Blade Mail, which can quickly kill Crystal Maiden if her ultimate is used while he is under its effect.

* Berserker's Call forces Mars to face in the direction choosen.
* Counter Helix deals pure damage and can go through Bulwark.

* Heroes with little health or magic resistance are easily picked off with Oracle's magic burst, such as Skywrath Mage, Crystal Maiden, or Enchantress.

* Heroes with high magical or pure damage will bypass Bulwark: Timbersaw, Dark Willow, Enigma, Invoker, Pugna, Skywrath Mage, Tinker, Zeus, Oracle.

* Any hero with a low HP pool is easy for Tinker to nuke down: Crystal Maiden, Enchantress, Gyrocopter, Lion, Riki, Techies, Terrorblade, Necrophos, Invoker.

* Heroes with high magical or pure damage will bypass Bulwark: Timbersaw, Dark Willow, Enigma, Invoker, Pugna, Skywrath Mage, Tinker, Zeus, Oracle.

* Heroes with slow movement speeds and small health pools (supports like Crystal Maiden or Witch Doctor) are easy targets for Phoenix. Should they be inflicted by its DOT debuffs, they will be very quickly killed without even getting a chance to fight back.

* Heroes with high health especially Strength heroes will take more damage on Sun Ray: Axe, Pudge, Bristleback, Mars.

* Lone Druid's early game is good against slow, squishy supports since his bear is very strong early game and an Entangling Claws proc almost always guarantees a kill: Ancient Apparition, Crystal Maiden, Shadow Shaman, etc.

* Nukers who have set amounts of damage will really struggle against Lone Druid especially in True Form: Puck, Void Spirit, Mars.

* Grave Chill will make Crystal Maiden's bad movement speed even worse.
* Soul Assumption charges can easily be stacked up from Freezing Field, allowing Visage to nuke enemies multiple times throughout the fight.
* {U:Familiar}'s Stone Form can also be used to interrupt Freezing Field, even while Crystal Maiden is under the effects of Glimmer Cape. Crystal Maiden must purchase a Black King Bar, which is far more costly.

* Battery Assault, Power Cogs, and Hookshot can interrupt Freezing Field, the latter two being able to go through invisibility should Crystal Maiden use Glimmer Cape.
* Rocket Flare can be used to find Crystal Maiden should she try to hide in the trees to try to safely cast Freezing Field.
* Hookshot allows Clockwerk to easily close in on Crystal Maiden and kill her.

* Crystal Maiden has a very bad movement speed, so Impale is easy to land against her. Furthermore, even while trapped by Frostbite, Nyx Assassin can still cast Impale.
* Crystal Maiden has very low armor, so Vendetta is very effective.
* Nyx Assassin has two ways to stop Freezing Field, provided she doesn't get a Black King Bar. He can either pop Spiked Carapace and simply walk into the field, or he can use Impale to interrupt the field, since Crystal Maiden has to channel it.
Additional:
* Spiked Carapace easily interrupts Freezing Field.
* Frostbite's damage over time sets up an easy Spiked Carapace stun.
* Crystal Maiden is extremely fragile and dies quickly to Nyx Assassin's burst damage.

* It is difficult for Mars to trade blows with Ogre Magi in the early game thanks to his high base health, resistance and Ignite.
* Bloodlust can assist Ogre Magi or an ally in repositioning against Mars for its move speed bonus.
* Fireblast can interrupt and mitigate Mars from performing his skill combos, especially in combination with Multicast.

* Rebound allows her to jump in or out of the Arena Of Blood. She can save her allies from the Arena with Dispose as well.

* Cold feet can be used to ensure that the full channel of Freezing Field doesn't go off.

* Arcane Orb's pure damage ignores Mars' Bulwark.
* Astral Imprisonment can be used to stop Mars from being disruptive or save allies from his abilities.
* Sanity's Eclipse deals high damage to Mars, due to his low intelligence pool.

* Crystal Maiden is squishy, is heavily spell reliant, has low base Intelligence, and is naturally slow, making her an ideal target for Silencer.
* Crystal Maiden's Freezing Field has a similar cooldown to Global Silence, therefore, Freezing Field can almost always be canceled to ruin aggressive Crystal Maiden initiations.

* Boulder Smash and Geomagnetic Grip allow Earth Spirit to easily disrupt Freezing Field, regardless of where Crystal Maiden is due to their incredible range. Earth Spirit is quite possibly the best hero for stopping long channeling abilities, and Crystal Maiden is vulnerable to him without a Black King Bar.
* All of Earth Spirit's spells allow him to easily close in on Crystal Maiden and kill her. Since she is a low health support, she generally stays behind in teamfights, but Earth Spirit can easily close the distance.
* Crystal Maiden has low movement speed and no other escape mechanism, rendering her extremely vulnerable to Earth Spirit's arsenal of long-range, damaging spells.

* Mars' own father is a formidable foe because Zeus deals massive amounts of magical damage. The high damage, low cooldown nukes of Arc Lightning and Lightning Bolt combined with the percent health magic damage of Static Field will shred Mars' health because it bypasses Bulwark completely.

* Heroes with a low health pool (Crystal Maiden, Skywrath Mage etc)

* Shadowraze deals magic damage and ignores Bulwark.
* Requiem of Souls deals magic damage and can fear Mars away, forcing him to turn around and therefore become vulnerable.

* Venomancer's spells all deal magical damage, ignoring Bulwark.
* Venomancer's multiple slows are especially effective at kiting Mars.
* Plague Ward can attack through Arena Of Blood.
Additional:
* Venomancer's poison attacks are all magical damage, ignoring Bulwark.
* Venomancer's multiple slows are especially effective against Mars' low mobility.
* Plague Wards can attack through Arena of Blood.

* Ball Lightning makes it almost impossible to catch Storm Spirit without someone else initiating for you.
* Overload is not reduced by Bulwark and the magical damage spam can wear down Mars quickly.
Additional:
* Storm Spirit's abilities all do magical damage, which can bypass Bulwark.
* Ball Lightning can escape through Arena of Blood and it is easy to dodge Spear of Mars.

* Even with Black King Bar or Linken's Sphere, Pudge's Meat Hook can still cancel Crystal Maiden's Freezing Field as she is a very easy target while channeling it.
* Pudge's Rot can make Crystal Maiden's already bad movement speed even worse.
* Many stacks of Flesh Heap will make it nearly impossible for Crystal Maiden to kill Pudge.
* Pudge's Dismember can also be used to cancel Crystal Maiden's Freezing Field, and alternatively, Pudge can also use it to save allies from getting killed by Crystal Maiden and heal them when upgraded with Aghanim's Shard.
* Crystal Maiden is prone to ganks in the lane or in the off-lane without proper vision. Pudge can take advantage of Crystal Maiden's lack of mobility, and gank her often.
Additional:
* Meat Hook can cancel Freezing Field, even if Crystal Maiden has Glimmer Cape.
* She is also slow and fragile, making her a good target for ganking.

* Gush can make Crystal Maiden's already weak armor even weaker.
* Kraken Shell can dispel Frostbite, preventing him from getting stuck inside Freezing Field.
* Ravage is very useful for interrupting Freezing Field, even while Crystal Maiden is under the effects of Glimmer Cape. Crystal Maiden must purchase a Black King Bar, which is far more costly.

* Nether Blast, Decrepify and Life Drain deal high magical damage and bypasses Bulwark.
* Nether Ward reduces the amount of abilities Mars can use during fights and forces Mars to be careful about the heavy mana cost of Arena Of Blood.
* Pugna is one of few heroes that can contest Mars' ability to push and defend towers early on.

* Ice Path allows Jakiro to easily cancel Freezing Field.
* Freezing Field makes Crystal Maiden an easy target for all of his abilities without a Black King Bar.
* With the Aghanim's Scepter upgraded Macropyre, Black King Bar becomes nearly useless for Crystal Maiden, as its high pure damage over time, long duration and ability to pierce spell immunity will either force Crystal Maiden to forcefully cancel Freezing Field or even discourage her from using it at all.
Additional:
* Ice Path allows Jakiro to easily cancel Freezing Field.
* Freezing Field makes Crystal Maiden an easy target for all of Jakiro's abilities without a Black King Bar.
* Aghanim's Scepter upgraded Macropyre can deal pure damage-over-time and pierce spell immunity, making Black King Bar nearly useless for Crystal Maiden, as its high damage over time and long duration can discourage Crystal Maiden to use Freezing Field. Remember, however, that Crystal Maiden can partially solve this issue by buying Aghanim's Shard, which will allow her to simply walk out of Macropyre.

* 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.

* Crystal Maiden is extremely fragile and she's an easy target for him. She has no real disables that can lock Ember Spirit down, and all of her skill damage can be negated with Flame Guard. The damage from Searing Chains, Flame Guard, and Sleigh of Fist can easily take her down.

* Heroes who rely on channeling abilities can be interrupted in teamfights by Rolling Thunder: Crystal Maiden, Pugna, Witch Doctor

* Swashbuckle is an auto attack and therefore ignores Mars' Bulwark.
* Shield Crash upgraded with Aghanim is an auto attack and therefore ignores Mars' Bulwark.
* Rolling Thunder makes him immune to magic, making Pangolier able to roll in and out of Mars' Arena Of Blood.

* Crystal Nova helps on farming while applies an area slow.
* Frostbite extends Rubick's lockdown duration while providing extra damage, also serves as a farming ability.
* Freezing Field deals much greater damage thanks to Arcane Supremacy in teamfights.
* Freezing Field is a channeling ability and therefore can be stolen easily.
* Crystal Maiden has no innate ability to interrupt Freezing Field, though it may not be the case for her teammates; Yet a well-times Telekinesis lift or drop can interrupt Freezing Field.
* Consider build items that strengthens Freezing Field, such as Aghanim's Shard, Black King Bar and Aghanim's Scepter to reach its full potential.

* Viscous Nasal Goo can hinder Crystal Maiden's already abysmal mobility, which allows Bristleback (or his teammates) to run her down and kill her.
* Bristleback frequently builds Blade Mail, which can quickly kill Crystal Maiden if her ultimate is used while he is under its effect.
* The passive part of Bristleback will trigger many, many times under the damage from Freezing Field, and as the stacks increase, the damage output from each successive cast (or proc) will eat away at Crystal Maiden's small HP pool.

* Phantom's Embrace can silence Crystal Maiden and disrupt Freezing Field's channeling. Her slow movement speed and fragile nature will also make her an easy target for Stroke of Fate and Ink Swell.

* Sacred Arrow can be used to interrupt Freezing Field from a safe distance, forcing her to cancel it to dodge or get hit.
* Crystal Maiden has very slow movement speed, making her an easy Sacred Arrow target.
* Crystal Maiden has low health and can easily be killed with an Aghanim's Scepter combo or just when hit with an arrow.
* If Frostbite has already been used, Mirana can Leap away even when slowed by Crystal Nova or Freezing Field.

* Sticky Napalm slows turn rate, making it difficult for Mars to face frontwards, where Spear of Mars and Bulwark are effective. In combination with Firefly, which deals magic damage, Batrider can make quick work of Mars.
* Flaming Lasso disables Mars while enemies re-position themselves behind Mars to avoid Bulwark.

* Smoke Screen effectively disables Crystal Maiden's channeling spell: Freezing Field.
* Due to her low health and armor throughout the game, Riki can kill her easily.

* Blink Strike gives bonus backstab damage and can bypass Bulwark. Defensively, it could be used to teleport away from Mars, especially while inside Arena of Blood.
* Smoke Screen can interrupt Mars' skill combos, especially when cast inside Arena of Blood.
* Tricks of the Trade can be used to evade Mars' skills, which have a slight delay to them. It could also be used to buy himself time while trapped inside of Arena of Blood.
Additional:
* Bulwark is generally irrelevant against Riki as he primarily deals bonus damage from behind.

* In general, heroes with AoE or long range disables (such as Faceless Void with Chronosphere, Pudge with Meat Hook and Elder Titan with Echo Stomp) hinder Crystal Maiden, preventing her from using Freezing Field to help her team in a fight.

* Heroes that can save their allies can be a big problem for Mars: Dazzle, Omniknight.

* Duel is a great initiation to target Crystal Maiden with, as it prevents her from using Freezing Field or any other abilities and allowing the enemy team to quickly kill her before she can aid her team in a fight.

* Legion Commander is both good and bad vs Mars, on the plus side she can dispel Spear of Mars with Press the Attack and is a good Silver Edge carrier. However, Mars is not an ideal Duel target, as Bulwark will force her to 1: Buy Silver Edge, and 2: Hit Mars with it before the Duel, allowing a skilled Mars to react, especially with Eul's Scepter of Divinity. In teamfights, Mars will happily draw attention after using his abilities, and tank the Duel with all spells on cooldown.

* Heroes with strong channeling spells like Crystal Maiden's Freezing Field, Bane's Fiend's Grip, and Enigma's Black Hole can easily be interrupted from a long range by Nether Swap, assuming they don't have a Linken's Sphere.

* Channeling heroes will not go well against Warlock, especially those who build Black King Bar as Warlock's ultimate ability stun goes through spell immunity. E.g.: Crystal Maiden, Witch Doctor, Enigma, etc.

* Ursa is a special mention because despite Bulwark diminishing most of the damage Ursa does, he is quite durable, especially with Enrage, discouraging the aggressive all-in playstyle of Mars; Ursa can simply not target Mars.

* Heroes with break abilities: Shadow Demon (with Aghanim's Scepter), Viper.

* Heroes that depend on disrupting fights with ability combos or big ultimate abilities are vulnerable to the long stun of Fiend's Grip: Disruptor, Death Prophet, Enigma, Faceless Void, Invoker, Lich, Magnus, Mars, Medusa, Outworld Destroyer, Phoenix, Puck, Queen of Pain, Shadow Fiend, Treant Protector, Underlord, Winter Wyvern, Witch Doctor, Zeus.

* Heroes with high magical or pure damage will bypass Bulwark: Timbersaw, Dark Willow, Enigma, Invoker, Pugna, Skywrath Mage, Tinker, Zeus, Oracle.

* In the same vein, heroes with silences — especially with the AoE ones like Death Prophet's Silence — can also prevent Crystal Maiden from being able to impact a fight.

* Heroes with high magical or pure damage will bypass Bulwark: Timbersaw, Dark Willow, Enigma, Invoker, Pugna, Skywrath Mage, Tinker, Zeus, Oracle.

* Heroes with channeled abilities can be interrupted by a long-range Fissure: Crystal Maiden, Witch Doctor, Bane, Pugna, Pudge.

* Heroes with high magical or pure damage will bypass Bulwark: Timbersaw, Dark Willow, Enigma, Invoker, Pugna, Skywrath Mage, Tinker, Zeus, Oracle.

* Long range disables are really effective against dangerous area controllers and channeling Heroes, like Enigma, Faceless Void or Crystal Maiden, as it may cancel them or prevent enemies from doing further damage while keeping Lion in a relatively safe distance in the warzone.

* Crystal Maiden's already low armor and easily interruptible ultimate, Freezing Field can make Slardar her worst nightmare. Crystal Maiden also often builds Glimmer Cape which is revealed by Corrosive Haze.

* Heroes with high magical or pure damage will bypass Bulwark: Timbersaw, Dark Willow, Enigma, Invoker, Pugna, Skywrath Mage, Tinker, Zeus, Oracle.

* Any hero with low mobility and max healthsuch as Silencer, Crystal Maiden etc.

* Heroes that can save their allies can be a big problem for Mars: Dazzle, Omniknight.

* Fragile supports who die in a few hits against Sven's high physical damage: Crystal Maiden, Vengeful Spirit, Dark Willow.

* Lucent Beam allows Luna to easily cancel Freezing Field.
* Without Black King Bar protection, Lucent Beam and Eclipse can make a short work out of Crystal Maiden's abysmal health.
* Skilled Luna will always buy Dust of Appearance, allowing her team to have a vision on Crystal Maiden while invisible and during channeling Freezing Field.
* Even with Black King Bar, Luna can still inflict considerable damage on Crystal Maiden with her attacks, which get empowered with Moon Glaives and Lunar Blessing, also smart and skilled Luna will buy Abyssal Blade to cancel Freezing Field even through Black King Bar in case of emergency. And since Crystal Maiden rarely buys Linken's Sphere, this can be a very big problem for her.
Additional:
* Lucent Beam allows Luna to easily cancel Freezing Field.
* Without Black King Bar protection, Lucent Beam and Eclipse can make a short work out of Crystal Maiden's abysmal health.
* Skilled Luna will always buy Dust of Appearance, allowing her team to have a vision on Crystal Maiden while invisible and during channeling Freezing Field.
* Even with Black King Bar, Luna can still inflict considerable damage on Crystal Maiden with her attacks, which get empowered with Moon Glaives and Lunar Blessing, also smart and skilled Luna will buy Abyssal Blade to cancel Freezing Field even through Black King Bar in case of emergency. Forcing Crystal Maiden to buy Linken's Sphere.

* Solar Guardian can save allies caught inside Arena of Blood.

* Puck has both Waning Rift and Dream Coil to stop Freezing Field's channel regardless of whether or not Crystal Maiden has a Glimmer Cape, as both spells fully affect invisible units.

* Doom alone can easily pick off Crystal Maiden since she is fairly fragile, even with using only basic attacks, Infernal Blade, and Scorched Earth.
* Doom prevents her from using any abilities in a fight, making her impact negligible.
* Devour allows Doom to acquire a stun, allowing him to cancel Freezing Field without having to use Doom.

* Heroes with a low attack speed or are fragile will find themselves unable to deal with Troll Warlord's high physical damage and attack speed, like Crystal Maiden or Sven.

* Crystal Maiden's low health pool and slow movement speed make her a tempting and easy target.
* However, it may be wise to build Black King Bar first before attempting to fight her alone, as she can disable you and retaliate with Freezing Field.

* Heroes with large health pools (Pudge) or good innate magic resistance (Anti-Mage) can be very problematic for Crystal Maiden, since even if they are under the effect of her ultimate for the entire duration, the damage output is simply not enough to kill or force them to retreat.

* As Crystal Maiden is squishy with very bad movement speed, Spectre can easily stay on Crystal Maiden with Haunt and Spectral Dagger.
* Late game, with enough farm, Spectre can withstand an entire Freezing Field, possibly even causing Crystal Maiden to kill herself from Dispersion.

* Heroes who can easily harass Crystal Maiden out of lane in the early game (Clinkz, Viper) can prevent Crystal Maiden from being able to level effectively, and can ultimately slow down her level 6, 12, and 18 to a point where enemy carries already have items to address her ultimate.

* Low mobility heroes: Heroes with no/little means of traveling fast have difficulty getting to/away from Bounty Hunter due to his slowing Jinada and hastening Track. Few examples of such heroes are: Crystal Maiden, Sniper, Ursa, Witch Doctor, etc.

Additional:
* Shuriken Toss's stun is useful for cancelling Freezing Field from a distance.
* Track can be used for revealing Crystal Maiden when she uses Glimmer Cape.
* Jinada does burst physical damage (which is even bigger if dealt under Track's crits), which is effective due to Crystal Maiden's low HP and armor.
* Bounty Hunter likes to stay hidden from the fight and is less likely to get caught by Crystal Maiden's spells.

* Fragile supports with low armor are always a good prey, also her Psionic Trap will wear down most attempts to flee with their built-in disables: Silencer, Crystal Maiden, Warlock, Ancient Apparition, Grimstroke, Witch Doctor

* Heroes with channeled abilities which Assassinate may cancel at long range: Witch Doctor, Crystal Maiden, Shadow Shaman, Pugna

* Heroes with low health are especially vulnerable to Marksmanship's high damage output: Clinkz, Crystal Maiden.

* Juggernaut and Lifestealer have abilities (Blade Fury and Rage respectively) that prevent Crystal Maiden from using her spells on them in the early game, before Black King Bar and other magical reduction is even an issue.

* Medusa's Stone Gaze forces Mars to choose between getting petrified, or turning his vulnerable back on Medusa.

* Firestorm and Pit of Malice are very disruptive in team fights, completely matching Mars especially since it can all be cast inside Arena Of Blood and also does percentage-based magical damage, negating Bulwark.
* Dark Rift can save any allies of Underlord trapped in Arena Of Blood.
* Atrophy Aura allows Underlord to lane against Mars quite well since he does not have the best base damage during the early game.
* Underlord is a common carrier of both Pipe of Insight and Mekansm/Guardian Greaves, allowing his team to combat Mars in the mid to late game.

* Innately fragile heroes will die almost instantly to Reality Rift while Chaos Knight has illusions active: Drow Ranger, Bane, Necrophos, Crystal Maiden.

* Heroes with low mobility that rely on spells: Zeus, Lina, Crystal Maiden.