This hex was inflicted on Fernando when he decided to leave his family, friends and sport to join a gang of delinquents and toughs: he let his fear -of becoming the mexican (criminal) stererotype that people expected him to be- become true, and embraced this bad decision he made.

He'll return human only when he'll understand that he's not a criminal nor a delinquent, and that the stereotype people pushed him down his throat was racist: his mexican ethnicity isn't a synonim for "bad" or "gangster", but it's a beautiful heritage instead.

Cadejo Malo:
The Cadejo are two mexican spirits that takes form of strange dogs with hooves. The black one is benign, helping humans in choices and bad situations, while the white one is malevolent and makes humans take bad decisions.

This curse was made by the white one, and makes Fernando go in the wrong path in every situation having choices. This particular feature can grant Fernando a berserker mode, where he lets his rage and wildness take over him and go on a bloody rampage.