Cavern of Hero's Defeat

Cavern of Hero's Defeat enters the battlefield
tapped. It doesn't untap during it's controllers
untap step.
When Cavern of Hero's Defeat enters the battlefield exile all cards from all graveyards.
Whenever Cavern of Hero's Defeat becomes untapped, exile target legendary creature.
{t}: add {b}{r}
{b}{r}{p/b}{p/b}{p/r}{p/r}: Untap Cavern of Hero's Defeat.