In his Lightside form, Leon is an anthropomorphic chameleon. His upper part of his body is turquoise, and his lower part of his body is lime green, and his belly is yellow. He has fushia eyes and has goggles on his face.
In his Shadowside form, he wears a mad scientist’s outfit and carries a doctor’s checkup around his neck. His eyes are orange with yellow irises, and his tongue is half pink, half purple, and has claws on his hands.
In his Shadowside form, Dr. Chameleon has the power to shapeshift into any creature he wants and copy their attacks.
Dr. Chameleon first appeared in SS023. He attacks the Shadowside Detective Agency when they confronted him. Jibanyan (Shadowside) attacks Dr. Chameleon but was no match when he shapeshifts into Jibanyan (Shadowside) himself to equally match his attack. Micchy tried to fight back, but was tossed out the window by Dr. Chameleon. Junior was summoned when he changed into Whisper himself, making Dr. Chameleon turn into Whisper. Jibanyan then gave the upper hand and defeats Dr. Chameleon. He then reverts to his Lightside form, Leon.
It was revealed that before Leon became a Yo-Kai, he was originally a human villain actor in TV shows, and was hated by most people because of his villainous actions. One day, when he attacked the hero of the TV show, he suddenly lost his balance and fell off on top of the skylight to his death. After his tragic story, Leon got three comments from his three fans, telling him he was a great actor. Delighted, Leon released the Handsomeness Aura back to his fans he previously stole. Then he gives his Ark to Ayame and takes off.
However, at the climax of the episode, Dr. Chameleon was tracked down by Shutendoji (Shadowside) for him kidnapping handsome men. Dr. Chameleon tries to beg for mercy, but Shutendoji kills him by strangling him.