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 this way. Then exile it.