Mesmeric Fiend

a Nightmare enters the battlefield — 151 cards in the game can cause this (Mesmeric Fiend is one).

1. Umbris, Fear Manifest — When Mesmeric Fiend enters, Umbris, Fear Manifest exiles a card from an opponent's library

an artifact is exiled — 336 cards in the game can cause this (Mesmeric Fiend is one).

1. Shard of the Void Dragon — When an artifact is exiled thanks to Mesmeric Fiend, Shard of the Void Dragon puts 2 +1/+1 counters on itself

1 other card cares about it too. These are the ones with the most connections.

a Horror deals combat damage — 382 cards in the game can cause this (Mesmeric Fiend is one).

1. Captain N'ghathrod — When Mesmeric Fiend deals combat damage, Captain N'ghathrod mills a card

a creature is exiled — 1,003 cards in the game can cause this (Mesmeric Fiend is one).

When a creature is exiled thanks to Mesmeric Fiend:

1. Ashnod's Intervention — brings a card back
2. Soulherder — puts a +1/+1 counter on itself

5 other cards care about it too. These are the ones with the most connections.

anything is exiled — 2,497 cards in the game can cause this (Mesmeric Fiend is one).

1. The War Doctor — When a creature, artifact, enchantment, instant, sorcery, planeswalker or battle is exiled thanks to Mesmeric Fiend, The War Doctor puts a time counter on itself

1 other card cares about it too. These are the ones with the most connections.

anything attacks — 17,934 cards in the game can cause this (Mesmeric Fiend is one).

When Mesmeric Fiend attacks:

1. Far Fortune, End Boss — deals 1 damage
2. Temmet, Naktamun's Will — draws you 1 card
3. Grim Javelineer — gives +1/+0
4. Invisible Woman — triggers
5. Caesar, Legion's Emperor — sacrifices a creature
6. Guide of Souls — triggers
7. Campsite Cuisine — sacrifices a Food
8. Gossip's Talent — triggers
9. Banon, the Returners' Leader — draws and discards
10. Toph, Earthbending Master — puts a counter on a permanent

112 other cards care about it too. These are the ones with the most connections.

a creature attacks — 17,934 cards in the game can cause this (Mesmeric Fiend is one).

When Mesmeric Fiend attacks:

1. Adaptive Omnitool — searches a library
2. Anthem of Rakdos — gives +2/+0
3. Kindred Discovery — draws you 1 card
4. Invasion of New Capenna // Holy Frazzle-Cannon — puts counters on a permanent
5. Chorale of the Void — brings a card back
6. Anim Pakal, Thousandth Moon — puts a +1/+1 counter on itself
7. Saw — sacrifices a creature
8. Gisa's Favorite Shovel — makes an opponent sacrifice a creature
9. Ultima Weapon — kills a creature an opponent controls
10. Total War — kills a creature

181 other cards care about it too. These are the ones with the most connections.

a creature blocks — 17,934 cards in the game can cause this (Mesmeric Fiend is one).

When Mesmeric Fiend blocks:

1. Mage Hunters' Onslaught — makes a player lose 1 life
2. Carnage Gladiator — makes a player lose 1 life
3. Barrow-Blade — strips abilities
4. Heat of Battle — deals 1 damage
5. Battle Strain — deals 1 damage
6. Favor of the Woods — gains you 3 life
7. Tide of War — sacrifices a creature
8. Dead-Iron Sledge — kills a creature
9. Dwindle — kills a creature
10. Shield of the Righteous — triggers

18 other cards care about it too. These are the ones with the most connections.

a nontoken creature attacks — 17,934 cards in the game can cause this (Mesmeric Fiend is one).

When Mesmeric Fiend attacks:

1. Mardu Ascendancy — makes a token
2. Basri Ket — makes a token
3. Militia's Pride — makes a token

a creature deals combat damage — 17,934 cards in the game can cause this (Mesmeric Fiend is one).

When Mesmeric Fiend deals combat damage:

1. Locutus of Borg — makes a token
2. Antagonist Incorporator — makes a token
3. Hive Mind Coprocessor — makes you lose life

194 other cards care about it too. These are the ones with the most connections.

a creature is cast — 18,010 cards in the game can cause this (Mesmeric Fiend is one).

When Mesmeric Fiend is cast:

1. God-Eternal Oketra — makes a token
2. Primeval Bounty — makes a token
3. Bloodbond March — brings a card back
4. Dancing from Dark to Dawn — puts that spell's mana value counters on a creature
5. Endrek Sahr, Master Breeder — makes that spell's mana value tokens
6. Summon: Fenrir — it arrives with counters thanks to Summon: Fenrir
7. Summon: Brynhildr — grants haste
8. Skittering Horror — sacrifices itself
9. Skittering Skirge — sacrifices itself
10. Skittering Monstrosity — sacrifices itself

81 other cards care about it too. These are the ones with the most connections.

a creature enters the battlefield — 19,800 cards in the game can cause this (Mesmeric Fiend is one).

When Mesmeric Fiend enters:

1. Slash, Reptile Rampager — deals 2 damage
2. Ray Fillet, Wave Warrior — puts a counter on itself
3. Bess, Soul Nourisher — puts a +1/+1 counter on itself
4. The Neutrinos — gets +1/+0
5. Wingnut, Bat on the Belfry — grants flying, haste and menace
6. Aetherstorm Roc — puts a counter on a permanent you control
7. Raphael, Most Attitude — exiles a card from your library

298 other cards care about it too. These are the ones with the most connections.

anything enters the battlefield — 26,499 cards in the game can cause this (Mesmeric Fiend is one).

1. Prowl, Stoic Strategist // Prowl, Pursuit Vehicle — When Mesmeric Fiend enters, Prowl, Stoic Strategist // Prowl, Pursuit Vehicle puts a +1/+1 counter on itself

39 other cards care about it too. These are the ones with the most connections.