Frankly I like the idea of true shapeshifting all by itself, in the lycanthropy style (not actually changing shape, purely mental). Skill shuffle is incredibly useful, moreso than most powers, although granted since most skills are in fact mental/social/technology based your base character has to pick a schtick in those areas and stick to it, only cranking in alertness, endurance, fists, whatever as needed. But it's pretty cool to be able to suddenly be alert or fast or strong or stealthy whenever such things are handy, with little opportunity cost (when you're sneaking, you usually can give up your perform or contacts skill...)
Of course you have to be a bit strange to be able to do that and not have your head explode. The idea I had along these lines was an agent of the Archive that was the opposite of her. He (always a he as she is always a she) could NOT learn human knowledge, but was entirely intuitive. (social skills in main form, various physical skills on demand, could never learn a skill like Scholarship or Burglar, although he'd speak the dominant language wherever he was). Like her, if the current version died it'd move on to a relative, wiping away their personality or at least forming most of it. He had a "guide my hand" type power which represented the Archive sending him into positions where he'd tip balance between future probabilities by being present in ways that suited her.
Another option might be a ghost or spirit of intellect actor, who got 100% into the various roles and probably had aspects that stuck them in those roles until snapped out of it.