Um, if you are using Persona straight from the game then you have to keep in line with the Arcana. In this case, Lucius wanted to use Lucifer the mythos not the actual Persona. So, I allowed it as long as none of the skill sets are not too OP. And you give me a reasonable explanation why they will be in the Arcana you are using. As Corporal said, the games are inconsistent. So As long as you give me a good reason, I will usually allow it unless I have some specific reason not too.