Hanging Castle of Kereth-Amin

The Hanging Castle of Kereth-Amin enters the battlefield tapped.
{t}: Add one mana of your commander's color identity.
{t}: Pay {4}. Search your library for an otherworldly card and put it on top of your library.

"A city on the edge of the Realm. It is guarded by abominations from the king's nightmares. Its noblest princes live in the castles of the cursed city."