Island of the Giant Pokemon - S1-E17
Revealing mistake: When Team Rocket is about to use the brakes in the cart, Jessie disappears from the cart, but her outline is still there. In the same shot, James overlaps her. Additionally, the cart is moving forward, but after Team Rocket breaks the brakes, it is moving backward. (00:16:09)
Island of the Giant Pokemon - S1-E17
Revealing mistake: When Jessie first saw pulling the cable, the phone is not fully coloured in, and the background can be seen through it. (00:13:08)
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.