Mushi Sanban is the evil younger sister of Numbuh 3 who loves everything she loves, but turns them all into horrific destruction after turning to the dark side.
Her true colors are revealed in "C.L.U.E.S." was when her family were going to a dinner party being host by Numbuh 2's mother to the Gilligan's house over one night. Mushi was jealous because her sister had a Posh Party Rainbow Monkey which sighed every time someone gave it a hug because she wanted that doll all to herself.
She decided that if she couldn't have that doll, then no one else would and when the lights went out, she took it from her sister and hugged it but she forgot one thing: The Posh Party Rainbow Monkey comes with deep care and share sighing. So she brutally stabbed the Posh Party Rainbow Monkey with a dinner fork which is found out by Hoagie. As a result, she was grounded for life with no hope for TV.
Later in "Operation: S.P.A.N.K.E.N.S.T.I.N.E.", Mushi digs up the Rainbow Monkey doll from its burial site at Plush Meadows Stuffed Animal Cemetery and brought it back to life as a Spankenstine Monster using Count Spankulot's powers, and sent it after Numbuh 2 as revenge for the previous incident. However, she was grounded and spanked by Count Spankulot for this, but is then seen escaping from her room with King Sandy.