The Pizza Monster.

The Pizza Monster is a combination of Carl's pizza and Dr. Dark and appears only in "Sleepless in Retroville". The pizza monster is aggressive. He also tries to eat children, but soon he gets scared of them. He only comes out at night because sun is his mortal enemy. 

At the end of the episode, it was revealed that he had a pizza wife and a pet pizza cat. He was voiced by Corey Burton.