Dusty Crevice

Dusty Crevice enters the battlefield tapped. Dusty Crevice does not untap unless you control or have exiled 3 or more Legendary cards.
When Dusty Crevice enters the battlefield, you may
pay {4}. If you do, choose target nonland permanent
an opponent controls. Exile it.
{4},{t}, You may cast cards exiled with Dusty Crevice
without paying their mana cast.