Horn Kombinen

As you cast this spell, you may discard any number of cards from your hand with the subtype "Kombinen" and pay
{w}{u}{b}. If you do, creatures you control get
+X/+X until end of turn, where X is the number of cards discarded in this way, and
you draw X cards. If you don't, creatures you control get +2/+0 until end of turn.