Retract

an artifact leaves the battlefield — 1,680 cards in the game can cause this (Retract is one).

1. Sludge Strider — When an artifact leaves the battlefield thanks to Retract, Sludge Strider makes a player lose 1 life

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

When Retract is cast:

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

When Retract is cast:

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

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