Fairy, Fairy, Quite Contrary - S1.E33

Prince Eccentro steal a lock and key (knowing that it might be a monster item) that kept Zazeus the Thunder Titan and Dragowing the Titan dragon imprisoned. Legend has it that when those two monsters clash, they create strong thunderstorms that would destroy the Earth Realm. The Mon Colle Knights must get the lock and key back and return it to the fairies that guard it before it's too late.