Massacre the Momentous

Unite {r} (You may cast this card for it's unite cost if you control a permanent of a color that this spell isn't.)
Abyssal - Massacre the Momentous deals 3 damage to each creature that entered the battlefield this turn. If you cast this from your hand, exile it. If you cast this from exile, it's blue and black in addition to it's other colors.
You may cast Massacre the Momentous from Exile.