Undo

a sorcery is cast — 3,720 cards in the game can cause this (Undo is one).

1. Spellweaver Volute — When Undo is cast, Spellweaver Volute copies a spell
2. Lilah, Undefeated Slickshot — When Undo is cast, Lilah, Undefeated Slickshot gets +1/+1
3. Niblis of Frost — When Undo is cast, Niblis of Frost gets +1/+1
4. Primeval Bounty — When Undo is cast, Primeval Bounty puts 3 counters on a creature
5. Tetsuko Umezawa, Pursuer — When Undo is cast, Tetsuko Umezawa, Pursuer gets +1/+1
6. Thor, God of Thunder — When Undo is cast, Thor, God of Thunder deals that spell's mana value damage
7. Krile Baldesion — When Undo is cast, Krile Baldesion brings a card back
8. Summon: Good King Mog XII — When Undo is cast, Summon: Good King Mog XII makes a token
9. Kykar, Wind's Fury — When Undo is cast, Kykar, Wind's Fury makes a token
10. Blood Funnel — When Undo is cast, Blood Funnel sacrifices a creature

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

a nontoken creature leaves the battlefield — 4,133 cards in the game can cause this (Undo is one).

1. Dual Nature — When a creature leaves the battlefield thanks to Undo, Dual Nature exiles a creature

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

a creature leaves the battlefield — 4,238 cards in the game can cause this (Undo is one).

When a creature leaves the battlefield thanks to Undo:

1. Extractor Demon — mills a card
2. Valor of the Worthy — makes a token
3. Traveling Plague — returns itself from the graveyard
4. Funeral March — makes a player sacrifice a creature

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

anything is cast — 31,128 cards in the game can cause this (Undo is one).

1. Windrider Wizard — When Undo is cast, Windrider Wizard draws you 1 card
2. Relic Amulet — When Undo is cast, Relic Amulet puts a charge counter on itself
3. Rockslide Sorcerer — When Undo is cast, Rockslide Sorcerer deals 1 damage
4. Umara Wizard // Umara Skyfalls — When Undo is cast, Umara Wizard // Umara Skyfalls grants flying
5. Alania, Divergent Storm — When Undo is cast, Alania, Divergent Storm makes an opponent draw 1 card
6. Umara Mystic — When Undo is cast, Umara Mystic gets +2/+0
7. Master of Winds — When Undo is cast, Master of Winds triggers

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