Krystal Dragon

As an additional cost to cast this spell, you must sacrifice 4 Sky Krystal creatures/artifacts or 1 Sky Guardian creature on the battlefield.
Flying, Vigilance, Trample
When Krystal Dragon enters the battlefield, gain
control of target creature an opponent controls.
Untap that creature. It gains flying until end of
turn.
When Krystal Dragon leaves the battlefield, exile
all non-land cards on the battlefield.