The Mouse Wizard appears in the episode "Little Brother." Kent encounters him while looking for some unbreakable ore, one of the three materials the blacksmith needs to make Kent a new sword. When Kent asks for some, the wizard instead offers him a "treasure of glittering emeralds," enough to be infinitely rich and to live the rest of his life in comfort. However, Kent says he's good and insists he wants the ore. The Mouse Wizard commends him on resisting his temptation, though Kent says he just does not care about money. The wizard then hands him the unbreakable ore (a bottle cap).
The Mouse Wizard has gray fur and wears a hooded cloak fastened with an emerald brooch. He is only ever seen inside a floating emerald, so it is unclear whether his eyes and cloak are actually green.