Other mistake: During the Pokérap, when the Poliwrath name is said, the Pokémon shown is actually Poliwag. Also, when the Graveler name is said, the Pokémon shown is actually Geodude.
Other mistake: Larvitar's weight is 158.7lb, but Ash can carry it in his backpack without any problems.
Plot hole: Pikachu repeatedly defeats Ground-type Pokémon with Electric-type attacks, despite the fact that Ground-type is supposedly immune to Electric-type moves.
Continuity mistake: In both "Attack of the Prehistoric Pokémon" and "Charizard Chills", Charizard carries Ash on his back without any trouble. However, later on in "Charizard's Burning Ambitions", Ash is suddenly too heavy for Charizard to carry.
Continuity mistake: In the early episodes of the Advanced Generation series, May is portrayed as being slightly taller than Ash. As the series moves on, May is consistently portrayed as being slightly shorter than him.
Answer: He is a good guy but just found himself in a bad situation when he worked for Lysander. He didn't want him to harm Ash and his Pokémon when he was trying to get the special bond between Ash and his Greninja to work. He does leave Lysander and go back to being a good person.