Krivitae, The Preserved

Whenever you cast a spell, each opponent loses
X life, where X is the number of spells you've
cast this turn.
{u}{b}{r}, {t}, Discard a card: Exile cards from the
top of target player's library until you exile two
nonland cards. You may cast those cards this
turn and you may spend mana as though it were
mana of any color. At the beginning of the next
endstep, return all cards in exile to their
owner's graveyard.