Continuity mistake: When Lance describes his mission to Ash, the glove on his disguise disappears. (00:16:37)
Continuity mistake: When Shelly says that Lance is not a Team Magma member, the gloves on her disguise disappear. (00:08:27)
Continuity mistake: When May and Max look at Lance's Gyarados, its red whiskers turn cream-coloured. (00:13:38)
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.