Original sentence: No firm definition has been offered in comics, but the term clearly refers to extraordinarily powerful mutants, such as Jean Grey, Vulcan, Rachel Summers, Iceman,  Storm (Iron Man #21) Elixir, Franklin Richards, and Emma Frost , among others
Edited sentence: No firm definition has been offered in comics, but the term clearly refers to extraordinarily powerful mutants, such as Jean Grey, Vulcan, Rachel Summers, Iceman,  Elixir, Franklin Richards, and Emma Frost , among others