Crosis, the Purger
Legendary Creature — Dragon
Flying
Whenever Crosis deals combat damage to a player, you may pay 
. If you do, choose a color, then that player reveals their hand and discards all cards of that color.
Pete Venters
Invasion (INV)
• #242Rulings
You choose the color during resolution. This means your opponent does not get to react after knowing the color you chose.
(wotc • 2004-10-04)
Rulings
You choose the color during resolution. This means your opponent does not get to react after knowing the color you chose.
(wotc • 2004-10-04)