Complex sentence: The other Xander possessed his more passive traits, including his sense of humor and fun, and was also highly insecure and paranoid, believing his double to be a demon who was hypnotizing his friends.
Split into simpler sentences: The other Xander possessed his more passive traits, including his sense of humor and fun. The second Xander was also highly insecure and believed his double to be a demon who was hypnotizing his friends.