Rejuvenation formula

The rejuvenation formula is a spell that can change one's age.

Mainstream Smurfs Media
Little is known of the ingredients or actual reversion of this spell. It is a vaguely detailed spell from one of Gargamel's books in "Gargamel's Second Childhood," with which he and Scruple switched ages by pulling apart a twisted cloth containing the necessary ingredients. The only way to reverse the spell was by recreating the process by which it first occurs.