Mimi is gnome in the Sidekick and Henchperson program at Hieronymous Wiggenstaff's School for Heroism and Villainy. They own a set of extending four foot long mechanical arms to make up for their short stature, which they seem to have made themself, as they let Fitzroy know they can "work something out" on commission when he inquires about getting a set for himself. They are first seen in episode 2 during Argo's blametaking class. They are described to wear traditional gnome attire complete with a cap (most likely Phrygian judging by the description)
They are also seen during the mission to aid the centaurs in episode 13 and 15.