The Sewer Monster looks like a mutated baby and has five limbs. The Sewer Monster is dark purple in color with a teal tongue.
When SpongeBob walks around town looking for something to write as an article on the newspaper, he sees a bank robbery, two muscled fish destroying a boatmobile, and then the Sewer Monster. Despite these interesting events, SpongeBob ignores them.
The monster resembles Insectosaurus from "Monster's vs Aliens"