Korshun, Rift Occultist

You may cast cards from any player's exile.
At the beginning of your upkeep, create
a 0/1 white blue black Cultist creature token with "{t}: Add {c} to your mana pool".
{3}{w}{u}{b}, {t}: Choose a card in your graveyard or a card you own from outside
the game and exile it.
Finders, keepers...