Ouroboroid

a creature gets a counter — 2,691 cards in the game can cause this (Ouroboroid is one).

1. Scurry Oak — When Scurry Oak gets a counter thanks to Ouroboroid, it makes a token
2. Fathom Mage — When Fathom Mage gets a counter thanks to Ouroboroid, it draws you 1 card
3. Hollowmurk Siege — When a creature gets a counter thanks to Ouroboroid, Hollowmurk Siege draws you 1 card
4. Ant-Man, Colony Commander — When a creature gets a counter thanks to Ouroboroid, Ant-Man, Colony Commander makes a token
5. Earth Kingdom General — When a creature gets a counter thanks to Ouroboroid, Earth Kingdom General gains you that much life
6. Casey Jones, Back Alley Brute — When a creature gets a counter thanks to Ouroboroid, Casey Jones, Back Alley Brute deals that much damage
7. Shalai and Hallar — When a creature gets a counter thanks to Ouroboroid, Shalai and Hallar deals that much damage
8. Danny Pink — When a creature gets a counter thanks to Ouroboroid, Danny Pink draws you 1 card
9. Enduring Scalelord — When a creature gets a counter thanks to Ouroboroid, Enduring Scalelord puts a +1/+1 counter on itself
10. Mikey & Leo, Chaos & Order — When a creature gets a counter thanks to Ouroboroid, Mikey & Leo, Chaos & Order draws you 1 card

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

anything gets a counter — 4,415 cards in the game can cause this (Ouroboroid is one).

1. All Will Be One — When a creature gets a counter thanks to Ouroboroid, All Will Be One deals that much damage
2. Lonis, Genetics Expert — When Lonis, Genetics Expert gets a counter thanks to Ouroboroid, it triggers

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

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

When Ouroboroid 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

113 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 (Ouroboroid is one).

When Ouroboroid 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

180 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 (Ouroboroid is one).

When Ouroboroid 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 (Ouroboroid is one).

When Ouroboroid 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 (Ouroboroid is one).

When Ouroboroid 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 enters the battlefield — 19,800 cards in the game can cause this (Ouroboroid is one).

When Ouroboroid enters:

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

301 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 (Ouroboroid is one).

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

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