Hystrodon

a creature is turned face up — 238 cards in the game can cause this (Hystrodon is one).

When Hystrodon is turned face up:

1. Printlifter Ooze — makes a token
2. Experiment Twelve — puts its power counters on a permanent
3. Pyrotechnic Performer — deals its power damage
4. Pine Walker — untaps a permanent
5. Fatal Mutation — kills it

a Beast creature is cast — 587 cards in the game can cause this (Hystrodon is one).

1. Tawnos, the Toymaker — When Hystrodon is cast, Tawnos, the Toymaker copies a spell

a Beast enters the battlefield — 632 cards in the game can cause this (Hystrodon is one).

When Hystrodon enters:

1. Totem Speaker — gains you 3 life
2. Wirewood Savage — draws you 1 card
3. Woodland Liege — draws you 1 card
4. Aether Charge — deals 4 damage

a card is drawn — 3,815 cards in the game can cause this (Hystrodon is one).

When Hystrodon makes a player draw a card:

1. Temmet, Naktamun's Will — gives +1/+1
2. Niv-Mizzet, Parun — deals 1 damage
3. Aether Syphon — mills a card
4. The Locust God — makes a token
5. Starving Revenant — makes each opponent lose 1 life
6. Diviner's Wand — gets +1/+1
7. Ominous Seas — puts a foreshadow counter on itself
8. Dream Trawler — gets +1/+0
9. Iron Man, Armored Avenger — puts a counter on a creature
10. The Astonishing Ant-Man — puts a +1/+1 counter on itself

57 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 (Hystrodon is one).

When Hystrodon attacks:

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

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 (Hystrodon is one).

When Hystrodon 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 (Hystrodon is one).

When Hystrodon 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 (Hystrodon is one).

When Hystrodon 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 (Hystrodon is one).

When Hystrodon 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

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 (Hystrodon is one).

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

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