Cleanliness is Next to Mondoness - S1.E38

Stench from Mondo after his soccer game and Professor Hiragi's bad breath from a sandwich he ate makes Kiki the Cleaner uncomfortable when Prince Eccentro stole her broom thinking it's a Monster Item. When they encounter Prince Eccentro near a river, he takes control of a Bone Dragon, a monster that can only be defeated by a magical creature. Mondo and Rockna go into the mind of a hippopotamus creature and with the magic cleaning broom back in Kiki's possession, Bone Dragon and Prince Eccentro is defeated.