Down By The River

When Down By The River enters the battlefield and at the beginning of your upkeep, you may search your library for an Ultimatum card or a card which color identity is {w}{u}{b}{r}{g}, reveal it and put it in your hand. Then shuffle your library.
{t}, Sacrifice target permanent you control: Add {w}{u}{b}{r}{g}
Lace your heart with mine
Let your sleeping soul take flight
Take me through the night
Down, down, down by the river