Vine-Covered Cave

Vine-Covered Cave enters the battlefield tapped.
When Vine-Covered Cave enters the battlefield,
look at the top 5 cards of your library, you may
choose a creature from them to exile under Vine-Covered Cave face-down.
{t}: Add {b} or {g} to your mana pool.
{x},{t}: Put the creature exiled with Vine-Covered
Cave onto the battlefield, it gains haste. X is the converted mana cost of the exiled creature.