This is a reference for the IE-defined mutant power levels.

[Alpha Level Mutants]
Alpha mutants suffer no permanent negative consequences of their mutations. The nature of their powers is largely potent and variable to be functional and useful in daily life and in self defense or combat. They are capable of relatively high levels of control exerted in the use of their powers and have no, or only minor, negative consequences in using their powers. They are, in general, more powerful than their similar Beta counterparts in the case that they share powers of the same nature.
-Jean Grey
-Logan/Wolverine
-Ororo Munroe/Storm
-Pietro Maximoff/Quicksilver
-Piotr Rasputin/Colossus
-Raven Darkholme/Mystique
-Tabitha Smith/Boom Boom
-X-23

[Beta Level Mutants]
Beta mutants may suffer minimal negative consequences of their mutations that are not solved within the nature of the powers themselves. Often, Beta level mutants are less powerful than their Alpha counterparts in similar powers, but may still be competent in the control of their powers at their level. On the other hand, some may be incapable of exerting control over their powers or unable to turn their powers off. Powers that require a specific alternate source for use may be classified as Beta level in the case that the sources are not a constant in most natural environments.
-Amara Aquilla/Magma
-Damon Valberg/Neuro
-Danielle Moonstar/Mirage
-Elizabeth "Liz" Braddock/Psylocke
-Il Sung Kim/Scrambler
-Jake Callaghan/Vellum
-Jean-Vivienne "Jean-Viv" Leclair/Scalpel
-Jubilation Lee/Jubilee
-Katherine "Kitty" Pryde/Shadowcat
-Lance Alvers/Avalanche
-Lorna Dane/Polaris
-Noel Leclair/Noel
-Paige Guthrie/Husk
-Shiro Yoshida/Sunfire
-Tatiana Caban/Catiana
-Terry Cassidy/Siryn
-Wanda Maximoff/Scarlet Witch

[Gamma Level Mutants]
Gamma mutants may be as powerful as Beta or even Alpha level mutants, but suffer severe consequences of their mutations. Often times but not always, these are physical mutations that make it impossible to survive in day to day life without making extreme changes from their previous life before the manifestation of their powers. These may also be powers that are constantly active and provide a notably negative consequence due to said constant activity.
-Beast/Hank McCoy
-Sunder/Carmine DiMauro

[Delta Level Mutants]
Delta mutants are generally less powerful than Alpha, Beta and Gamma mutants. They may or may not have control over these powers, but in general the powers have limited versatility.
-Chameleon/Sadie Slade
-Jalapeno/Ileana Ruiz