Fervor

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

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

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

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

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

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

a creature it applies speed increase to — 19,392 cards in the game can cause this (Fervor is one).

1. Pollywog Prodigy — Fervor gives Pollywog Prodigy haste
2. Havengul Lich — Fervor gives Havengul Lich haste
3. Saheeli, Radiant Creator — Fervor gives Saheeli, Radiant Creator haste
4. Captain Jean-Luc Picard — Fervor gives Captain Jean-Luc Picard haste
5. Windrider Wizard — Fervor gives Windrider Wizard haste
6. Master of Winds — Fervor gives Master of Winds haste
7. Sokka, Bold Boomeranger — Fervor gives Sokka, Bold Boomeranger haste
8. Invisible Woman — Fervor gives Invisible Woman haste
9. Rockslide Sorcerer — Fervor gives Rockslide Sorcerer haste
10. Umara Wizard // Umara Skyfalls — Fervor gives Umara Wizard // Umara Skyfalls haste

19,382 other cards care about it too. These are the ones with the most connections.