Overseer, Arbiter of Ascension

Changeling

When Overseer enters, you may search your library for a card, exile it face down, then shuffle.

{w}{u}{b}{r}{g},{t}: You may cast a spell from among cards exiled with Overseer, Arbiter of Ascension, without paying its mana cost, if you do, exile Overseer, Arbiter of Ascension, then return it to the battlefield under its owner’s control.