Satoshi and Butterfree! Until the Day We Meet Again!! - S16-E33
Continuity mistake: In one shot of Ash and his friends helping Caterpie, Caterpie's yellow tail turns green like the rest of its body. (00:10:12)
Satoshi and Butterfree! Until the Day We Meet Again!! - S16-E33
Revealing mistake: In the close-up of Ash and Metapod running to the cliff at night, part of Metapod is cut off several times. (00:15:12)
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.