Cruelty

As you cast this spell, you may sacrifice a creature. If you do, this spell’s mana cost is reduced by that creature’s mana value. When this creature enters, if {U}{U}{U} was spent to cast it, draw three cards, then discard a card. When this creature enters, if {B}{B}{B} was spent to cast it, each opponent discards two cards at random. When this creature enters, if {R}{R}{R} was spent to cast it, it deals 4 damage to target creature or player. Players dealt damage this way can’t gain life for the rest of the game.