Crosis, the Purger

Legendary Creature - Dragon 6/6, 3UBR (6)
Flying

Whenever Crosis, the Purger deals combat damage to a player, you may pay {2}{B}. If you do, choose a color, then that player reveals his or her hand and discards all cards of that color.¹
Illus. Pete Venters

Gatherer Card Rulings [Nov 2009]

• 10/4/2004: You choose the color during resolution. This means your opponent does not get to react after knowing the color you chose.

Format Legality	Legal in Vintage, Legacy, MTGO Classic Banned in Extended, Standard
Printings (1/6)	Invasion (Rare)