nope theresNope, there are no limits,,,. fromFrom the most ridiculous power, gaseous form as noted, to the most extreme. proteusProteus could alter time and space at his will , in exiles comics he sought to also be able to cross through dimensions. heHe was the first one to be sawnseen to have such unlimited powers. even krakoaEven Krakoa the living island was just a huge mutant but not even in comparison with what powersetpower set Proteus had. afterAfter that, many have followed, cocludingincluding in general in the Omegal lvlOmega level mutants category: muttantsmutants with powers of cosmic scale. so came Mickhail rasputinRasputin (brother of colosusColossus) with energy absorbing and redirection power. theyThey have lvledleveled up the scarlet witch to extreme powers. Jaime Braddock (elder brother of Psylocke) had the ability to pull and shape the strings of reality. Nathan summers (Cable) that his powers were turned down cause of the technovirus in him (in a saga the virus is gone and Cable goes Godlike powers, he is in risk of his life getting sooooo powerfullpowerful so he downgrades himself again). Franklin Richards (son of MisterfantasticMister Fantastic and the Invisible womanWoman) has had Celestial lvllevel powers since being a little kid . andAnd sooo many others. evenEven Jean Grey is omega lvlOmega level on her own, Phoinex force wouldntPhoenix Force wouldn't choose a random host , it craves for power...
soSo NO limits at all...choose Choose a set of powers and just pump it on a little teenager and wonders will happen,,,.