Lefty, Righty, and Slim are the nefarious three headed monster who hosts the Goosebumps Triple Header books.
Lefty likes to create scares, or something worse. He has sharp teeth, a lizard-like face, and a Mohawk.
Righty is very cautious, he wears glasses, and has combed hair, which may indicate that he's the smart one.
Don't think for a minute you can get away from him. Slim is the center head (possibly making him the leader). He has a completely bald head and huge sharp bottom teeth.