Ooh, awesomely horrible ideas time. First off, how do you want the memories from Lancer to bleed in? Because he has memories of his life as Cu Chulainn as well as memories from his version of the Grail War and of the short while he's been in the tower. Second off, he's so totally going to abuse all of Jeanne's abilities. Using Charisma for seduction, etc. He'll even try to boss the other Servants around because he's Ruler now.