I think my first answer for this would have to be Ultra the Multi-Alien. maybe stick him in a new R.E.B.E.L.S. team with Captain Comet, Vril Dox, Starfire, Jessica Cruz, Crush and New-52 style Captain Atom... maybe Hawkgirl, or Blackfire, if I couldn't use Kory... and failing either of those, I'd just create a new female Tamaranean or Thanagarian character