Leonardo is the assistant of the Witch on top of Horned-Owl Mountain. He either fights or gives a riddle to anyone trying to enter the Witch's house.
Leonardo was guarding the entrance to his boss's cave when he encountered Paifu and Mr. Maruyama who came for the medicine needed to cure After arriving to Horned-Owl Mountain. When he encounters the two asks that in order to retrieve the medicine the need for the "Monster-Flu", he lets them know that they either need to fight him or solve a riddle. When he learns that Mr. Maruyama identity as "The Volcano" he decides to have them solve a riddle. However he unintentionally gives the pair an easy riddle. After they answer correctly he takes them to his master. While meeting his monster the witch request that that Leonardo brings the medicine. When asked if they should deliver it so that could they learn about the cost of the medicine being 15,000 yen. When revealing the price of the medicine they need they workout an arrangement for the medicine with the challenge having to lift his master. Mako Maruyama attempts he challenge as requested but fails to lift her. Paifu later attempts this by being turned into his were-koala form. After succeeding Leonardo and the witch agree to send the medicine to Batwing Ridge Village.