Kenjaku, Mastermind

Select a non-creature spell from your deck. Reveal it. This card may be your background, except that after it leaves the battlefield, it cannot return to your command zone.

When a creature an opponent controls dies while Kenjaku, Mastermind, is on the battlefield, put an experience counter on it. You may cast creatures
from graveyards with experience counters using
mana as if it were mana of any color to cast them.