Trostani, Choir of the Void

Emerge {3}{g}{w} (You may cast this spell by sacrificing a creature and paying the emerge cost reduced by that creature's mana value.)

Trostani can’t be blocked by nontoken creatures.

Whenever a creature deals combat damage to one of your opponents, its controller creates a 0/1 Eldrazi Spawn creature token with “Sacrifice this creature:
Add {c}.”