This all got rolling around in my head, because I want to use Iman Abdulmajid (David Bowie's wife) as a PB SO BADLY that I've been researching how I could do it in a way that fits with the game.
I'm going to use Spectrum (Monica Rambeau) with the powers of Cloak. I'd mix her background with that of Cloak's in order to achieve what I'm looking for. I ask about Daggerm because I have to have a Dagger character to feed her, of course. I want to play her as an older member of the staff (Iman will be 60 on July 25th) who has great control of her power so that she doesn't have to be in cloak form all the time. Also, it would be pure mutation rather than drug-induced powers.
I'd like to say that she and her Dagger partner were "superheroes" during the 70s. More like urban legends of New York rather than known mutants, but joined with Xavier when he picked them out telepathically. This matches up with the timeline note on mutants being urban legends.