J. Pastor, Unveiler of Secrets

{1}{u}{u}: Search your library for a card and exile
it face down with a mystery counter on it, then
shuffle your library.
At the beginning of each player's upkeep, that
player may choose a card exiled with a mystery
counter on it and pay {3}. If they do, turn that
card face up. If it's a spell, that player casts it
without paying it's mana cost. If it's a land, that
player puts it onto the battlefield under their
control.