Thusios, Demon of Sacrifice

Bestow {2}{b}{b} (This card is an aura until removed)
Flying
Enchanted creature or Thusios has:
Tribute 4 - When Thusios enters the battlefield as an aura or becomes a creature, you must destroy two target creatures if Tribute is not paid each time.
If Thusios detaches to become a creature, pay {4}{b}{b} or return him to your hand.