S1E22: Attack of the Headless Horror

When Fred's favorite adventurer, Dr. Rick Spartan, starts teaching biology at the Crystal Cove's High School, the gang gets to meet him. Fred tells him that the gang has also been into some terrifying experiences, Spartan immediately invites them to have dinner at his place, where he promises to show them his latest trophy, the cursed Shrunken Head of Squar Gringot. But when its headless body appears and threatens to pursue the professor until the end of his days for plundering its tomb, the gang must find out a way to break the curse.