Merfolk Crypt
Land (Rare)

Merfolk Crypt enters the battlefield tapped unless you reveal an enchantment card from your hand.

Tap: Add U or B to your mana pool.

Put Merfolk Crypt on top of your library: Add 1 to your mana pool.

1U: Merfolk Crypt becomes a 1/1 blue and black Cephalid creature with flying until end of turn. It's still a land.

Allan Staples