After Derek's brother dies in a crash, Derek finds that there is a way to bring him back to life however this results in summoning the vengeful god known as Kalfu (Corey Feldman) being summoned, Kalfu promises him he'd be able to see his brother again but there is a price, Kalfu needs to use Derek's body for his means of carrying out his plan and so he uses his dark powers to possess him and Derek finds himself becoming Kalfu.

Kalfu is from this movie here:
https://www.imdb.com/title/tt2091455/