A Chain of Whirlpool Islands! A Renewed Challenge!! - S5-E1
Continuity mistake: When Professor Elm affirms to the fact that the Corsola with him is his, the land on the map changes from three shots before. (00:07:10)
A Chain of Whirlpool Islands! A Renewed Challenge!! - S5-E1
Continuity mistake: When Marius says, "Why don't we give these kids a chance to rest up a bit after the experience they've just had?" his left arm is bent to the right, but in the next shot, it is bent upward. (00:07:52)
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.