Crosis, the Purger is a rare Legendary Creature — Dragon card from The List (PLST), collector number C17-168. Current market price: $2.62, TCGplayer market prices via Scryfall.
Flying Whenever Crosis deals combat damage to a player, you may pay {2}{B}. If you do, choose a color, then that player reveals their hand and discards all cards of that color.