true potential

you drive an Ethereal key into the heart of anyone within arms reach of you, that person unlocks their maximum potential for the duration of their next turn ( if that someone or something is multiclassing they become level 20 in every class they are multiclassing into ). If you unlock a monster's full potential it's challenge rating is doubled ( it's hit point's, and hit dice will be doubled )  but will be considered an ally for the duration of it being unlocked. you can only cast this spell once per month