The Mouse Knight appears in the episode "Little Brother." Kent meets him while on a quest for a clod of mystic earth, one of the three materials required for Kent's new sword. The knight says he has some but instead offers Kent one of his beautiful daughters to wed. Kent declines, saying all he cares about is fighting bad guys. The Mouse Knight then spits in the dirt and scoops up some mystic earth.
The Mouse Knight wears a suit of bronze armor that covers everything but his hands and head. He wields a (relatively) gigantic sword.