Arboria

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

When Arboria 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 (Arboria is one).

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

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

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

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