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

* Mana Burn is strong against Keeper of the Light due to his high mana pool.
* Spiked Carapace can be used to reflect Illuminate damage and stun Keeper of the Light.
* Vendetta allows Nyx Assassin to follow Keeper of the Light around if he tries to split-push.

* 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.
Additional:
* 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.

* Heroes with teleports to escape Will-O-Wisp: Phantom Assassin, Puck, Queen of Pain, Storm Spirit

* 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.

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

* Heroes with dispels: Legion Commander, Oracle, Slark

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

* 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.

* Mars has no way to trade with Ogre Magi in the early game thanks to his high base health, resistance and Ignite.
* Once Ogre Magi gets level 2 he may also have Bloodlust, which makes him even harder to deal with in lane.
* Fireblast can be ridiculously strong later on in the game for controlling Mars.
* Spear of Mars, which is Mars' main source of damage in the early game, cannot guarantee kills early on Ogre Magi.

* 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.

* Venomancer's spells all deal magical damage, ignoring Bulwark.
* Venomancer's multiple slows are especially effective at kiting Mars.
* Plague Wards 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.

* 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.

* Berserker's Call forces Mars to face in the direction choosen.
* Counter Helix is a much stronger lane trader than Spear of Mars.

* Mars' own father is a formidable foe because Zeus deals mostly 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.

* 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.

* 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.

* 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:
* Nethertoxin breaks Bulwark entirely, making Mars far less tanky. Using Nethertoxin inside Arena of Blood may discourage enemies from following up with Mars' initiation.
* Rod of Atos is currently common on Viper and keeps Mars in position long enough to be killed.
* Viper is not very tanky earlier in the game, so positioning against Mars is important since a well-timed Spear of Mars can be the end of Viper.

* Sticky Napalm slows turn rate, making it difficult for Mars to control the direction he is facing to activate Bulwark.
* Flaming Lasso disables Mars while enemies re-position themselves behind Mars to avoid Bulwark.

* 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.

* If Mars lanes middle, Shadow Fiend can keep the lane pushed against him.
* Shadow Fiend can go an entirely magical based build, which is very effective against Mars.

* Rage allows him to dispel Blinding Light from himself.
* Open Wounds allows him to slow and kill Keeper of the Light.

* Low health spellcasters: Lina, Witch Doctor, Tinker, Keeper of the Light, all rely heavily on their spells and are fragile heroes. They all also have avoidable spells, allowing Puck to get to them and quickly burst them down.

* Heroes that wish to disrupt fights with spell combos or big ultimates 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.

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

* Heroes that can jump and kill him: Meepo, Clinkz, Templar Assassin

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

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

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

* Ursa is a special mention because despite his high physical damage attacking from the front won't achieve much against Mars but isn't a great target for Mars either since Ursa is very resistant to damage with Enrage so there isn't much that can be done to stop Ursa from going on your team.

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

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

* Mana Drain is very effective against heroes that have mana burn abilities such as Anti-Mage, Nyx Assassin and Keeper of the Light.

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

* Heroes with teleports to escape Will-O-Wisp: Phantom Assassin, Puck, Queen of Pain, Storm Spirit

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

* Squishy heroes, usually supports, like Io, Ancient Apparition, Keeper of the Light etc can die instantly from Tiny's magic burst.

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

* Bulwark is generally irrelevant against Riki as he primarily deals bonus damage from behind.
Additional:
* Blink Strike gives bonus backstab damage. Along with Tricks of the Trade it completely bypasses Bulwark.

* Crippling Fear prevents Keeper of the Light from using his spells to keep his team alive during team-fights.
* Dark Ascension is very strong against Keeper of the Light, who relies on daytime to be effective.
Additional:
* Keeper of the Light's Aghanim's Scepter upgrade loses much of its power, due to Night Stalker being able to reduce the duration of daytime by a lot.

* 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.
Additional:
* 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.