* 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.

* 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.

* Undying's Tombstone will cheerfully chew through treants, incidentally netting you some extra income during fights.
* The above interaction tends to ensure that skirmishes are heavily populated with units, thereby buffing Soul Rip

* Firestorm makes quick work of Treants and Atrophy Aura gives him temporary damage for every Treant killed.
* Pit of Malice can stop Teleportation channeling.
* Atrophy Aura greatly reduces Nature's Prophet's damage and he has no other good way to deal damage.
* Fiend's Gate can counter split-pushing, which is something that Nature's Prophet relies on a lot.

* Due to Spirit Breaker's low attack speed, Tombstone is problematic for Spirit Breaker.
* The zombies summoned from Tombstone apply a stacking movement speed slow, which can significantly reduce Greater Bash's damage.
* Soul Rip and Decay allows Undying and his allies to survive from incoming ganks of Spirit Breaker.

* Pit of Malice can be cast in the path of Spirit Breaker's Charge of Darkness to cancel it.
* Dark Rift provides a way to escape from a gank for Underlord and his teammates.

* Undying's Decay is a dangerous ability against Bristleback, as it makes him more vulnerable and reduces his tankiness.
* Undying's Tombstone together with Flesh Golem can slow Bristleback down significantly.

* Pit of Malice prevents Phantom Assassin from either escaping or engaging with Phantom Strike.
* Phantom Assassin's damage output is entirely physical, therefore Atrophy Aura Atrophy Aura is very hazardous for her in most of the stages, particularly since it also affects Coup De Grace Coup de Grace, hindering Phantom Assassin's main source of damage.
* Without proper items and any area-of-effect ability/item, Phantom Assassin cannot stop Underlord and his team to escape with Fiend's Gate, nor she can intercept them if Underlord chooses to teleport on any area of the map.
Additional:
* Pit of Malice prevents Phantom Assassin from either escaping or engaging with Phantom Strike.
* Phantom Assassin's damage output is entirely physical, therefore Atrophy Aura Atrophy Aura is very hazardous for her in most of the stages, particularly since it also affects Coup De Grace Coup de Grace, hindering Phantom Assassin's main source of damage.
* Without proper items and any area-of-effect ability/item, Phantom Assassin cannot stop Underlord and his team to escape with Fiend's Gate, nor she can intercept them if Underlord chooses to teleport on any area of the map.

* Undying can use Decay not only to reduce Sven's maximum health, but also to reduce the damage he can deal with his ultimate.
* Zombies spawned by Tombstone together with Flesh Golem slow Sven down significantly. Landing Sven's powerful but somewhat slow right-click on Tombstone would be a waste.

* In general, attacks of the melee heroes who are entirely reliant on dealing physical damage and/or have very little to no area-of-effect abilities will make Underlord tickle and will have no effect against him, and will be unable to ambush Underlord and his team if Underlord chooses to use Dark Rift to get to a designated point of the map: Phantom Assassin, Terrorblade, Troll Warlord, Drow Ranger, Phantom Lancer, Chaos Knight, Sven, Wraith King, Bounty Hunter, Alchemist, Templar Assassin, Nyx Assassin, Bane.

* Undying saps strength from heroes with Decay, and Ogre Magi's high strength gain will allow Undying to steal more and more strength, becoming stronger with each use.
* Due to the Strength steal from Decay, Undying is normally very tanky, and has high health, making it harder for Ogre Magi to kill him.

* Damage reduction from Atrophy Aura prevents Bloodseeker from killing targets and gaining his Thirst bonuses.
* Pit of Malice's area of effect catches Bloodseeker easily, negating his speed bonus during teamfights.
* Dark Rift allows Underlord to transport Ruptured allies to the fountain, rendering it useless.

* Dark Rift allows Underlord to transport allies from poison damage-over-time to the fountain.
* Underlord usually buys Pipe of Insight that gives a magic resistance to allies, inhibiting the damage from Venomancer abilities.

* Atrophy Aura reduces Drow Ranger's damage significantly, as she relies on agility to be effective.

* Decay can be good against Centaur Warrunner, as reducing the health of Centaur can make Double Edge risky.
* His zombies do not proc Retaliate, as it only procs for regular attacks.

* Atrophy Aura's percentage-based damage reduction greatly diminishes Legion Commander's overall damage output, even if she has won many Duels
* Legion Commander cannot get out the way of Firestorm because she is stationary.
Additional:
* Atrophy Aura makes it hard for Legion Commander to win Duels.
* Fiend's Gate can be used to save Underlord and his allies from a Duel or to intercept Legion Commander, because outside from Overwhelming Odds, Legion Commander has no other area-of-effect abilities.

* Firestorm will easily clear Chen's creeps.
* Pit of Malice will trap Chen and render him helpless.
* Atrophy Aura gives bonus damage to Underlord for each killed creep and weakens Chen's damage.
* Fiend's Gate can counter Chen's pushing attempts, and he has nothing to intercept it.

* Spectre must chase for kills and relies on movement speed for mobility in fights, and has no way to counter the Tombstone zombies.
* The potency of Soul Rip can be increased from nearby illusions from Haunt.
* Decay will shut down Spectre during the laning phase by effectively cutting down her initial health pool.
Additional:
* Spectre must chase for kills and relies on movement speed for mobility in fights, and has no way to counter the Tombstone zombies.
* The potency of Soul Rip can be increased from nearby illusions, so Undying can use Haunt against Spectre.
* Early game Decay will make Spectre easy to shut down in lane.

* Pit of Malice prevents Riki from casting Blink Strike. or Tricks of the Trade.
* Atrophy Aura reduces Riki's damage.
* Firestorm can be used to harrass Riki in lane.

* Firestorm's percentage damage can quickly demolish the Spirit Bear's high HP
* Pit of Malice will allow allies to easily kite Lone Druid due to his low mobility

* Underlord's Atrophy Aura reduces Morphling's high base damage gained through agility shift.

* In general, heroes with long cooldowns on their abilities or ultimate will struggle against the relentless pressure provided by Dark Rift or Fiend's Gate (Requires Aghanim's Scepter): Terrorblade, Dragon Knight, Omniknight.

* Heroes with a slow attack rate will find themselves struggling to take out Tombstone, like Doom.

* In general, melee heroes without blink mechanisms or spell immunity will have a hard time positioning against Pit of Malice: Sven, Tiny, Wraith King, Dragon Knight, Meepo, Doom, Bounty Hunter, Dark Seer, Undying, Alchemist, Legion Commander.

* 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

* Heroes that reduce the damage that Marci can deal during her ultimate, like Razor, Rubick, Bane, Dragon Knight and Underlord.

* 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.

* In general, melee heroes without blink mechanisms or spell immunity will have a hard time positioning against Pit of Malice: Sven, Tiny, Wraith King, Dragon Knight, Meepo, Doom, Bounty Hunter, Dark Seer, Undying, Alchemist, Legion Commander.

* In general, attacks of the melee heroes who are entirely reliant on dealing physical damage and/or have very little to no area-of-effect abilities will make Underlord tickle and will have no effect against him, and will be unable to ambush Underlord and his team if Underlord chooses to use Dark Rift to get to a designated point of the map: Phantom Assassin, Terrorblade, Troll Warlord, Drow Ranger, Phantom Lancer, Chaos Knight, Sven, Wraith King, Bounty Hunter, Alchemist, Templar Assassin, Nyx Assassin, Bane.

* 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.

* Anti-Tank heroes like: Razor, Necrophos, Undying.

* In general, attacks of the melee heroes who are entirely reliant on dealing physical damage and/or have very little to no area-of-effect abilities will make Underlord tickle and will have no effect against him, and will be unable to ambush Underlord and his team if Underlord chooses to use Dark Rift to get to a designated point of the map: Phantom Assassin, Terrorblade, Troll Warlord, Drow Ranger, Phantom Lancer, Chaos Knight, Sven, Wraith King, Bounty Hunter, Alchemist, Templar Assassin, Nyx Assassin, Bane.

* In general, attacks of the melee heroes who are entirely reliant on dealing physical damage and/or have very little to no area-of-effect abilities will make Underlord tickle and will have no effect against him, and will be unable to ambush Underlord and his team if Underlord chooses to use Dark Rift to get to a designated point of the map: Phantom Assassin, Terrorblade, Troll Warlord, Drow Ranger, Phantom Lancer, Chaos Knight, Sven, Wraith King, Bounty Hunter, Alchemist, Templar Assassin, Nyx Assassin, Bane.

* Heroes with AoE abilities will hit Slark in Shadow Dance: Lina, Jakiro, Underlord, Leshrac, Dark Seer, Earthshaker, Timbersaw, Crystal Maiden.

* In general, melee heroes without blink mechanisms or spell immunity will have a hard time positioning against Pit of Malice: Sven, Tiny, Wraith King, Dragon Knight, Meepo, Doom, Bounty Hunter, Dark Seer, Undying, Alchemist, Legion Commander.

* In general, heroes with long cooldowns on their abilities or ultimate will struggle against the relentless pressure provided by Dark Rift or Fiend's Gate (Requires Aghanim's Scepter): Terrorblade, Dragon Knight, Omniknight.

* Atrophy Aura reduces Terrorblade's damage significantly, even during Metamorphosis.
* Firestorm deals significant damage to Terrorblade and his illusions from a safe distance.
* Pit of Malice can keep Terrorblade and his illusions under control.
* Fiend's Gate can either bail out Underlord's team away from a bad engagement against a Terrorblade under Metamorphosis or caught Terrorblade off guard if he is not careful, and besides Reflection, Terrorblade has no other abilities to intercept Underlord nor his team when they use it to start a teamfight.
* Likewise, Fiend's Gate can be used to quickly move Underlord's team to the frontlines, to strike Terrorblade and his allies during Metamorphosis's 150 seconds of cooldown.
Additional:
* Atrophy Aura reduces Terrorblade's damage significantly, even during Metamorphosis.
* Firestorm deals significant damage to Terrorblade and his illusions from a safe distance.
* Pit of Malice can keep Terrorblade and his illusions under control.
* Fiend's Gate can either bail out Underlord's team away from a bad engagement against a Terrorblade under Metamorphosis or caught Terrorblade off guard if he is not careful, and besides Reflection, Terrorblade has no other abilities to intercept Underlord nor his team when they use it to start a teamfight.
* Likewise, Fiend's Gate can be used to quickly move Underlord's team to the frontlines, to strike Terrorblade and his allies during Metamorphosis's 150 seconds of cooldown.

* Firestorm will destroy Refraction charges very quickly.
* Firestorm will hit Templar Assassin while under the effects of Meld Meld.
* Templar Assassin has a hard time maneuvering around Pit of Malice.

* In general, attacks of the melee heroes who are entirely reliant on dealing physical damage and/or have very little to no area-of-effect abilities will make Underlord tickle and will have no effect against him, and will be unable to ambush Underlord and his team if Underlord chooses to use Dark Rift to get to a designated point of the map: Phantom Assassin, Terrorblade, Troll Warlord, Drow Ranger, Phantom Lancer, Chaos Knight, Sven, Wraith King, Bounty Hunter, Alchemist, Templar Assassin, Nyx Assassin, Bane.

* In general, attacks of the melee heroes who are entirely reliant on dealing physical damage and/or have very little to no area-of-effect abilities will make Underlord tickle and will have no effect against him, and will be unable to ambush Underlord and his team if Underlord chooses to use Dark Rift to get to a designated point of the map: Phantom Assassin, Terrorblade, Troll Warlord, Drow Ranger, Phantom Lancer, Chaos Knight, Sven, Wraith King, Bounty Hunter, Alchemist, Templar Assassin, Nyx Assassin, Bane.

* Winter Wyvern cannot handle the Zombies created by Undying's Tombstone very well. In most situations, Zombies will have more movement speed than her.
* Undying can gain one or two easy Decay stacks on an ally in Cold Embrace. The ally will still take the damage as well.
Additional:
* Winter Wyvern cannot handle the Zombies created by Tombstone very well. In most situations, Zombies will have more movement speed than her.
* Undying can gain one or two easy Decay stacks on an ally in Cold Embrace. The ally will still take the damage as well, since it is magical.

* Atrophy Aura decreases Troll Warlord's damage.
* Pit of Malice helps lock down Troll Warlord.
* Battle Trance disallows Troll from running out of both Firestorm and Pit of Malice.

* Heroes with abilities that can save teammates are also effective such as Shadow Demon, Dazzle, Oracle, Bane, Pugna, Tusk, Winter Wyvern, Io, Underlord, Treant Protector and Keeper of the Light.

* In general, melee heroes without blink mechanisms or spell immunity will have a hard time positioning against Pit of Malice: Sven, Tiny, Wraith King, Dragon Knight, Meepo, Doom, Bounty Hunter, Dark Seer, Undying, Alchemist, Legion Commander.