Continuity mistake: When Misty says, "I wouldn't be surprised if the next gym leaders are tougher than the last ones," the right strap of Tracey's rucksack is on his collar, but in the next shot, it is not. Also, the marks on Ash's cheek go from looking like zs to looking like two pairs of lines. Additionally, his mouth is open, but in the next shot, it is closed. (00:01:42)
Other mistake: When Meowth is reading about the trophy, he has five lines on his charm instead of four. (00:03:30)
Other mistake: When Meowth shifts his eyes from his book about the trophy to the trophy, he has five lines on his charm instead of four. (00:04:11)
Other mistake: When Team Rocket is running away with the trophy, James falls flat on the ground, and an indentation of his body as well as the trophy is made. The indentation shows a perfect match to the trophy, but James' arms were partially covering it, so there shouldn't be a perfect indent of the trophy in the ground. (00:05:18)
Continuity mistake: When Tracey wonders why everyone is outside the museum, the black straps on his bag turn orange, like the rest of the bag. (00:05:29)
Revealing mistake: As Ash, Misty, and Tracey are making their way through the crowd, Tracey clips through one of the people in it. (00:05:33)
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.