Brainstorm

a card is drawn — 3,815 cards in the game can cause this (Brainstorm is one).

When Brainstorm makes a player draw a card:

1. Temmet, Naktamun's Will — gives +1/+1
2. Niv-Mizzet, Parun — deals 1 damage
3. Aether Syphon — mills a card
4. The Locust God — makes a token
5. Starving Revenant — makes each opponent lose 1 life
6. Diviner's Wand — gets +1/+1
7. Ominous Seas — puts a foreshadow counter on itself
8. Dream Trawler — gets +1/+0
9. Iron Man, Armored Avenger — puts a counter on a creature
10. The Astonishing Ant-Man — puts a +1/+1 counter on itself

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

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

When Brainstorm is cast:

1. Lunar Mystic — draws you 1 card
2. Ojer Pakpatiq, Deepest Epoch // Temple of Cyclical Time — grants rebound
3. Repeated Reverberation — copies an ability
4. Riku of Two Reflections — copies a spell
5. Sword of Wealth and Power — copies a spell
6. Lilah, Undefeated Slickshot — gets +1/+1
7. Gale, Waterdeep Prodigy — brings a card back
8. Harness the Storm — 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 (Brainstorm is one).

When Brainstorm 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.