Stain first appears as the leader of a group of dogs that rule over the seafood district. He antagonized Peppy, the focus pup of the episode, when the pup got his foot stuck in a grate. Deciding to scare and try harming the pup for trespassing in his territory, Stain advances on the trapped Peppy, only to be interrupted by the arrival of the Pound Puppies. Through a series of trip-ups, Strudel and Niblet manage to defeat Stain and humiliate him by dropping the scruffy dog into a tank of fish guts. Stain immediately lost all respect as a tough dog following this and the Pound Puppies, especially Strudel, gained a reputation as superheroes. Angered by this change of events, Stain swears revenge on all of them, becoming something of a "supervillian" in the episode's superhero theme.
Towards the episode's conclusion, Stain abducts Peppy as the pup goes with Strudel and Niblet on their superhero mission. Using Peppy as bait, Stain manages to (rather easily and quickly) defeat both Strudel and the other Pound Puppies (sans Niblet) and entrap them all in a net dangled over a tank of fish guts, in the same manner as a supervillain intending to kill his enemies. Despite being brushed off by Strudel, who had let her superheroine status get to her head, Niblet charges in and, by accidentally sitting on a tack, defeats Stain and frees Peppy and his friends. Humiliated once again, Stain comes clean and admits much of his behavior is derived from a desire for attention, which he feels he cannot gain from a human due to his scruffy appearance and surly demeanor. Nevertheless, the Pound Puppies set him up to be adopted by a similarly scruffy security guard, effectively giving Stain a new home and removing his motivation for bullying.