I Was a Teenage Bigfoot is a short story in The Dresden Files series by Jim Butcher. It is set around the time of Dead Beat. It was originally published in Blood Lite 3: Aftertaste, and was later included in the anthologies Working for Bigfoot and Brief Cases.
Being a scion he has more than his fair share of life force, and has therefore attracted the attention of Dr. Fabio, the dean of Saint Mark's Academy for the Gifted and Talented, who needs some to fight the ravages of Middle Ages. An ex-Venator, he attempts to use black magic, prompting Dresden to interfere and break the spell.