Card

Warstorm Surge

Mana cost {5}{R}

Whenever a creature you control enters, it deals damage equal to its power to any target.

Part of 103 known combos, 11 of them two-card. 2 official rulings.

Bracket

B1 Exhibition — Not in the same deck as its two-card combo partners: Polyraptor, Vrondiss, Rage of Ancients, Hornet Nest, Raptor Hatchling, Storm Herd, Overgrown Armasaur, Broodhatch Nantuko, Sporeweb Weaver, Sekki, Seasons' Guide, Saber Ants, Nested Ghoul
B2 Core — Not in the same deck as its two-card combo partners: Polyraptor, Vrondiss, Rage of Ancients, Hornet Nest, Raptor Hatchling, Storm Herd, Overgrown Armasaur, Broodhatch Nantuko, Sporeweb Weaver, Sekki, Seasons' Guide, Saber Ants, Nested Ghoul
B3 Upgraded — Not in the same deck as its early two-card combo partners: Hornet Nest, Raptor Hatchling, Overgrown Armasaur, Broodhatch Nantuko, Sporeweb Weaver, Saber Ants, Nested Ghoul
B4 Optimized — allowed: No restriction beyond the banned list
B5 cEDH — allowed: No restriction beyond the banned list

Two-card combo with Polyraptor, Vrondiss, Rage of Ancients, Hornet Nest, Raptor Hatchling, Storm Herd, Overgrown Armasaur, Broodhatch Nantuko, Sporeweb Weaver, Sekki, Seasons' Guide, Saber Ants, Nested Ghoul (early with Hornet Nest, Raptor Hatchling, Overgrown Armasaur, Broodhatch Nantuko, Sporeweb Weaver, Saber Ants, Nested Ghoul)

Bracket: Lotus Vault analysis, with Commander Spellbook flags

103 known combos, 11 of them two-card.

Polyraptor + Warstorm Surge
Produces: Infinite death triggers, Infinite creature ETB, Infinite creature LTB
View on Commander Spellbook
Vrondiss, Rage of Ancients + Warstorm Surge
Produces: Infinite death triggers, Infinite creature ETB, Infinite creature LTB
View on Commander Spellbook
Miirym, Sentinel Wyrm + Bladewing the Risen + Warstorm Surge
Produces: Infinite creature LTB, Infinite creature ETB, Infinite death triggers
View on Commander Spellbook

2011-09-22 · Wizards of the Coast
Warstorm Surge is the source of the ability, but the creature is the source of the damage. The ability couldn't target a creature with protection from red, for example. It could target a creature with protection from creatures, but all the damage would be prevented. Since damage is dealt by the creature, abilities like lifelink, deathtouch and infect are taken into account, even if the creature has left the battlefield by the time it deals damage.
2011-09-22 · Wizards of the Coast
The creature that entered deals damage equal to its current power to the targeted permanent or player. If it's no longer on the battlefield, its last known existence on the battlefield is checked to determine its power.

Rulings: Scryfall · Wizards of the Coast