So I got the iPad version of Sentinels of the Multiverse and one of the things that struck me was that Legacy's powers are very much about helping others.
In Mutants & Masterminds, I'd do it by leaning heavily on the Usable by Others modifier, with the advantages Inspire (pretty much made for it) and I'd probably use Favored Environment (With Teammates), or, if the GM disallowed that, put together a lot of Favored Environments and Favored Foes as Enhanced Advantages, usable by others. Then you wouldn't have to worry about power level limitations. Add Regeneration Usable by Others, and then build a tough scrapper with what's left.
In ICONS, you don't have the power level limitation to worry about, but it is harder. One way to do it might be Ability Increase Extra: Affects Others. (If the GM objects, you could do it as Ability Boost, with the caveat that you suffer the ability loss because you've been "lending" your strength to others.) Again, some Healing or Regeneration Extra: Affects Others.
In Supers, you'd want Healing, of course, and I think the best choice would be Imbue with the boost for Multiple Targets.