David, Perceptive Apprentice

When David enters the battlefield, choose
an opponent to become your mentor.
Whenever your mentor casts a non-creature spell,
draw a card.
Whenever you cast a spell, your mentor creates a treasure token.
{b}{u}, {t}: Exile a card from your mentor's
graveyard. You may cast it and spend mana as
though it were mana of any color to cast it for
as long as it remains exiled.