Thrax, Proctor of Madness

Flying, Cascade
Instants, sorcery, and planeswalker spells you
cast cost {u}{b}{r} less to cast.
Magecraft - Draw a card, then discard a card.
{u}{b}{r}{t}: Gain control of target creature with
mana value X or less where X is the amount
of instant or sorceries in your graveyard.