Mouser

Mouser was one of the many villains from Super Mario Bros. 2 that never appeared again.

In Boo's Pizza
In Boo's Pizza, Mouser is basically Wart's right-hand man as regent of Hyrule while he's off searching for the Wind Fish. Mouser lost Hyrule multiple times before securing it with the aid of King Dedede, Ganondorf Dragmire, and Bowser. Mouser was later involved in quelling a Goron rebellion around the time Wart became the sole Emperor of Gaia and left his brother Martin as regent. At some point, Mouser died and returned as "Mouser the White", a reference to both The Lord of the Rings and Doki Doki Panic.

In Boo's Pizza II, Mouser was among Wart's Grande Armee during the final hunt for the Wind Fish. Mouser, realizing Wart's insanity, betrays him by allowing Cayde free access to the inner workings of the Doomship. However, Wart, using their psychic link, discovers the treachery. Deciding to make Mouser useful at last, Wart executes the fat rat by tossing him off of the ship and into the maw of the Wind Fish as an attempt to lure it in for a final attack. However, Wart's killing blow is cucked by a distracting Daggertooth on the island below.