7. The Leviathan on Supernatural
Supernatural generally takes a minimalist approach to its vast rogues gallery of monsters. Instead of going all out on make-up and costumes, the show's angels, demons and the like simply possess humans, and all the audience gets is the occasional kooky-colored eyes as an indicator.
The seventh season villains, the Leviathan, follow the same rote execution, with one added detail: a hidden set of razor sharp teeth that allude to their biblical description. The result: respectable sentiment, but distractingly bad execution.