YMMV / Billy and Mandy in: Trepanation of the Skull and You

• Fanon: A popular bit of fanon regarding this short is that it's a direct prequel to the series—Billy's trepanation is what ended up making him stupid, while Mandy, in a rare show of remorse, never smiled again and became considerably less sociable.
• Nightmare Fuel: The short film is surprisingly unsettling. It's a jarring departure from the cartoonishness of Maxwell's later work, with a very creepy atmosphere.