Primordial Hydra

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

When Primordial Hydra gets a counter:

1. Hollowmurk Siege — draws you 1 card
2. Ant-Man, Colony Commander — makes a token
3. Earth Kingdom General — gains you that much life
4. Casey Jones, Back Alley Brute — deals that much damage
5. Generous Patron — draws you 1 card
6. Shalai and Hallar — deals that much damage
7. Danny Pink — draws you 1 card
8. Enduring Scalelord — puts a +1/+1 counter on itself
9. Bold Plagiarist — puts counters on a permanent
10. 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 (Primordial Hydra is one).

1. All Will Be One — When Primordial Hydra gets a counter, All Will Be One deals that much damage

8 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 (Primordial Hydra is one).

When Primordial Hydra 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 (Primordial Hydra is one).

When Primordial Hydra 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 (Primordial Hydra is one).

When Primordial Hydra 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 creature deals combat damage — 17,934 cards in the game can cause this (Primordial Hydra is one).

When Primordial Hydra deals combat damage:

1. Primo, the Unbounded — makes a token
2. Locutus of Borg — makes a token
3. Antagonist Incorporator — makes a token
4. Hive Mind Coprocessor — makes you lose life

193 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 (Primordial Hydra is one).

When Primordial Hydra attacks:

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

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

When Primordial Hydra enters:

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

302 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 (Primordial Hydra is one).

1. Prowl, Stoic Strategist // Prowl, Pursuit Vehicle — When Primordial Hydra 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.