Karsuin's Astral Diviner

Whenever you cast a multicolored spell, exile the top card of your library.
During each turn, you may play up to one card exiled with Karsuin's Astral Diviner without paying its mana cost, and may cast it as though it had flash if that card is a spell.
{2}{w}{u}{b}{r}{g}, {t}: Exile the top four cards of your library.