From Dota 2 Wiki
- Dispel Magic from Storm instantly removes Guardian Angel from Omniknight's allies in its radius of effect.
- Doom turns Omniknight into a walking creep, or completely takes out his buffed cores, also removing Guardian Angel in the process.
- Doom has access to Satyr Banisher's Purge, also allowing him to remove Guardian Angel.
- Tornado purges Guardian Angel from multiple targets.
- EMP depletes Omniknight's already small mana pool.
- Invoker's many disables keep Omniknight's team occupied until Guardian Angel times out.
- Even if Eclipse is blocked by Repel, it won't be blocked by Guardian Angel, allowing Luna to finish off Omniknight's team while her team focuses on a single Repelled enemy.
- Song of the Siren can be used to time out Guardian Angel, giving Naga Siren's team an easy opportunity to counter-initiate.
- Since Song of the Siren doesn't affect magic immune units, it can be used to disable the rest of Omniknight's team while her team focuses on a single Repelled enemy.
- Fortune's End's AoE purge will remove Guardian Angel.
- Arcane Orb's pure damage penetrates Guardian Angel's defense.
- Outworld Devourer's intelligence steal is also devastating to Omniknight's already low mana pool.
- Unstable Current will purge Omniknight's buffs from any ally in a 350 AoE around Razor every 5 seconds.
- All of Omniknight's abilities are valuable for Rubick to Spell Steal, and Omniknight has no throwaway ability to cover his last used spell.
- Demonic Purge will remove Omniknight's buffs.
- 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.
- Heroes with large magical AoE damage will fare well against Omniknight: Lich, Ancient Apparition, Jakiro, Disruptor
- Heroes with abilities that go through spell immunity render Omniknight much less useful: Black Hole, Reverse Polarity, Primal Roar
- Heroes who can harass Omniknight out of lane will keep him weak in the mid game: Viper, Venomancer, Clinkz
- Heroes who can drain mana can make Omniknight useless after he uses one or two abilities: Lion, Keeper of the Light, Anti-Mage, Phantom Lancer
- Orchid Malevolence and other items that can prevent the casting of abilities makes Omniknight useless.
- Eul's Scepter of Divinity and Nullifier's can purge Guardian Angel.
- Abyssal Blade's stun and bash pierces Repel's spell immunity.
- Omniknight's healing prevents allies from dropping low enough for Culling Blade. However, it can still go through all his buffs.
- Axe also enjoys getting close to allied heroes in order to damage them with his Counter Helix, which can easily be punished by Purification.
- Phantasms can be easily killed with Purification.
- Guardian Angel works well against Chaos Knight's overwhelming reliance on physical burst damage.
- Exorcism's damage is blocked by Guardian Angel.
- Omnislash is blocked by Guardian Angel.
- Both Guardian Angel and Purification are perfect counters against Duel.
- Guardian Angel completely counters Winter's Curse if he is able to cast it.
- Heroes who rely strongly on melee physical damage will fare badly against Omniknight's Guardian Angel: Sven, Phantom Assassin, Juggernaut, Dragon Knight, Lycan, Ursa, Troll Warlord
Works well with...Clockwerk
- A Purification on Clockwerk while he's fighting inside Power Cogs will turn the fight in Clockwerk's favor.
- Arcane Aura solves Omniknight's mana problems, and Omniknight can keep her protected in return with Repel and Guardian Angel during her Freezing Field. Her slows and root also pair well with Degen Aura and Purification.
- Chakra Magic solves Omniknight's mana problems.
- A successful Meat Hook is an easy set-up for a Purification.
- Omniknight can also negate the self-damage of Rot with Repel.
- Phantom Strike places Phantom Assassin in position Omniknight to follow up with an offensive Purification.
- Repel can be used as an alternative to a Black King Bar, freeing up gold for Phantom Assassin to buy damage items.
- Repel allows Shadow Fiend to channel Requiem of Souls in the midst of the enemy team without relying on Black King Bar.
- Ball Lightning let's Storm Spirit get close for an easy Purification.