Quick and Easy Questions (please read the OP)

[Handsome Jack]

Ideally, you'd not summon a copy of a person who already exists here, even if from another continuity/reality/whathaveyou. Because: why not just write WITH the person who is already here? However, by RAW: Secondaries are... well, they're "fakes" for lack of a better way to put it. They're the summoner's mental image of that person. So, say you wanted to have Cell as a Secondary. You absolutely could. It could even be exactly like MY Cell. Because it's a fake made from your mental image.

But again, please consider using the resources that are already here before you decide that you'd rather write with your idealized version of Mickey than with the PC/NPC who is already here.