The Ratagator is a large, mutated creature, resembling a mixture of both a rat and an alligator, hence its name (though its more pointed snout makes it more resemble a crocodile). The Ratagator also happens to be a friend of Mario and Luigi in The Super Mario Bros. Super Show!, often appearing to visit them in their home in Mario Brothers Plumbing.
The Ratagator's first appearance in The Super Mario Bros. Super Show! is in the live-action segment "Alligator Dundee," where the Ratagator, having been frightened by something in its sewer home, rushes into Mario Brothers Plumbing, where it encounters Mario and Luigi. Seeing the Ratagator distressed, Mario and Luigi comfort it and learn that something had frightened it, only to be surprised when the Ratagator quickly speeds away back into the sewer upon the arrival of a man named Alligator Dundee.
Later, Alligator Dundee, who is revealed to be hunting the Ratagator, enters its sewer home in search of it while Mario and Luigi, having surmised that Alligator Dundee is what frightened the Ratagator earlier, reluctantly help him. Finding the Ratagator, Alligator Dundee, having seemingly failed to lure it out into the open with a tuna sandwich, seemingly gets into a skirmish with, but seemingly succeeds in getting the Ratagator to try and chase him out of the sewer.
In the end, it is revealed to Alligator Dundee, after being accidentally captured in a net by Mario and Luigi, that the Ratagator is their pet; learning this, Alligator Dundee decides to stop his hunt for the Ratagator and creates a major motion picture detailing his hunting of it, while also deciding to rename himself "Ratagator Dundee." The Ratagator, having heard Alligator Dundee say its name, rushed forwards out of the sewer and, along with letting Mario and Luigi pet it, it also allows Alligator Dundee to pet it as well.
The Ratagator next makes a small appearance in "Mario Hillbillies," where it allows the visiting Ellie Mae to pet it; when Ellie Mae asks Mario Joe and Luigi Bob, who are posing as their cousins, Mario and Luigi, what the Ratagator's name was, the two respond with the names "Zeke" and "Luke."
Similarly, the Ratagator plays a small role in the following episode, "Baby Mario Love," where it appears, carrying a leash in its jaws, trying to convince Mario to take it for a crawl, which Mario refuses to do, stating he has already taken the Ratagator for a crawl earlier; later, as Mario attempts to tell Luigi that their lives lack glitz, glamor and a certain "je ne sais pas," Luigi, apparently not comprehending Mario's last statement, tells him to watch his mouth, saying the Ratagator is present.
It is also featured in "Tutti Frutti, Oh Mario," where it is first seen with Luigi, who thinks it is making some strange noises, while that is actually Little Robert singing. After Luigi realizes it is not the Ratagator singing, it goes away, but returns at the end of the episode having eaten the tape Luigi used to record Little Robert singing. The Ratagator is then heard imitating Little Robert's song.