Sardonyx, Valiant Warhammer

Fusion--When this creature enters the battlefield, exile a creature named Pearl, Crystal Aegis and a creature named Garnet, Renegade Fusion. If you don't, return Sardonyx to its owner's hand.
Whenever Sardonyx attacks, if there are 2 or more other attacking creatures, untap all creatures you control. They gain flying and double strike until end of turn.
When Sardonyx dies, return the exiled creatures to the battlefield under your control.