Endless Horizons

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

1. The War Doctor — When a Plains is exiled thanks to Endless Horizons, The War Doctor puts a time counter on itself

an enchantment is cast — 3,673 cards in the game can cause this (Endless Horizons is one).

When Endless Horizons is cast:

1. Hallowed Haunting — makes a token
2. Daxos the Returned — puts a counter on a permanent
3. Tatsunari, Toad Rider — makes a token
4. Sythis, Harvest's Hand — gains you 1 life
5. Sigil of the Empty Throne — makes a token
6. Dawnhart Geist — gains you 2 life
7. Herald of the Pantheon — gains you 1 life
8. Kami of Transience — puts a +1/+1 counter on itself
9. Argothian Enchantress — draws you 1 card
10. Mesa Enchantress — draws you 1 card

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

a nontoken enchantment enters the battlefield — 3,691 cards in the game can cause this (Endless Horizons is one).

1. Historian's Boon — When Endless Horizons enters, Historian's Boon makes a token

an enchantment enters the battlefield — 3,743 cards in the game can cause this (Endless Horizons is one).

When Endless Horizons enters:

1. Calix, Guided by Fate — puts a counter on a creature
2. Elvish Archivist — draws you 1 card
3. Victor, Valgavoth's Seneschal — surveils
4. Strength from the Fallen — gives +X/+X, where X is the number of creature cards in your graveyard
5. Doomwake Giant — shrinks a creature by -1/-1
6. Cacophony Unleashed — turns something into a creature
7. Ghostly Dancers — makes a token
8. Thassa's Devourer — mills a card
9. Killian, Decisive Mentor — taps a creature
10. Thoughtrender Lamia — makes an opponent discard a card

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