Valgarix, Apex of the Night

Mutate {3}{u/b}{w}{w}
—
Flying, Menace
Whenever this creature mutates, look at the
top three cards of target opponent's library.
Exile one card and put the rest into their
graveyard. As long as that card is exiled,
you can cast it, and you can spend mana
as though it were mana of any color to
cast it.