Seeker

an Aura enters the battlefield — 1,257 cards in the game can cause this (Seeker is one).

1. Tanglespan Lookout — When Seeker enters, Tanglespan Lookout draws you 1 card
2. Chishiro, the Shattered Blade — When Seeker enters, Chishiro, the Shattered Blade makes a token

1 other card cares about it too. These are the ones with the most connections.

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

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

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

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

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

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