Lefty, Righty, and Slim

Lefty, Righty, and Slim are the nefarious three headed monster who hosts the Goosebumps Triple Header books.

Lefty
Lefty likes to cruise up scares, or something worse, he has sharp teeth, a Lizard-like face, and he has a Mohawk.

Righty
Righty is here to tell you, something is defiantly wrong, he wears glasses, and has combed hair, which may indicate that he's the smart one.

Slim
Don't think for a minute you can get away from him, he is the center head (possibly making him the leader) with a completely bald head and huge sharp bottom teeth.

Trivia
He was the mascot of this series, and the third Goosebumps mascot overall, The other two being Curly the Skeleton and Slappy the Dummy.