Oh, there's an odd concept

Well, not odd in the sense of "new theory" but odd in the sense that I can't recall seeing it in a character before.

So Legacy is the latest in a long, long line of superheroes, and her ability is to manifest the powers of any of her super-powered ancestors. How would you do that in ICONS specifically or any game system generally?

It probably isn't Alter-Ego because that either limits the number of alter egos or forces them to be random. You'd want a defined list of ancestors, and "long, long line" might mean twenty ancestors...

So as a GM, I'd probably want to see a list of ancestors.

Maybe it would best be done as the Magic power--you take a panel to commune with the ancestors and then manifest the powers.

Of course, this could be considered a variation of the Transformation power, where the power level sets an upper limit on your abilities, so it might be Transformation (Ancestors) 8.

Or it's kinda like the Nemesis power.

Anyway, there are a number of precedents for an alter-ego kind of power that isn't Alter Ego.

(Watch, it'll turn out to have been done as an Adversaries character who I am not remembering.)