Thwart

an instant is cast — 3,931 cards in the game can cause this (Thwart is one).

1. Electro, Assaulting Battery — When Thwart is cast, Electro, Assaulting Battery adds 1 mana
2. Lunar Mystic — When Thwart is cast, Lunar Mystic draws you 1 card
3. Ojer Pakpatiq, Deepest Epoch // Temple of Cyclical Time — When Thwart is cast, Ojer Pakpatiq, Deepest Epoch // Temple of Cyclical Time grants rebound
4. Repeated Reverberation — When Thwart is cast, Repeated Reverberation copies an ability
5. Riku of Two Reflections — When Thwart is cast, Riku of Two Reflections copies a spell
6. Sword of Wealth and Power — When Thwart is cast, Sword of Wealth and Power copies a spell
7. Lilah, Undefeated Slickshot — When Thwart is cast, Lilah, Undefeated Slickshot gets +1/+1
8. Gale, Waterdeep Prodigy — When Thwart is cast, Gale, Waterdeep Prodigy brings a card back
9. In the Eye of Chaos — When Thwart is cast, In the Eye of Chaos counters a spell
10. Niblis of Frost — When Thwart is cast, Niblis of Frost taps a creature an opponent controls

427 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 (Thwart is one).

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

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