Goblin Pyromancer is a rare Creature — Goblin Wizard card from Onslaught (ONS), collector number 206. Current market price: $0.76 (foil $20.91), TCGplayer market prices via Scryfall.
When this creature enters, Goblin creatures get +3/+0 until end of turn. At the beginning of the end step, destroy all Goblins.