The Grim Adventures of Billy & Mandy - Season 6 Episode 6 -

While Billy was trying to dig his way to the Earth's core, he stumbles upon a frozen caveman. It's Fred Flintstone! Grim and Billy thawed him out of the ice. Grim wants to reap Fred's soul, but Billy wants to keep him as a friend. At school, he presented the caveman to the class. Then Fred goes crazy and kidnaps Mrs. Butterbean.