How do you measure a mutant superpower when it can't be boiled down to simple hard numbers like top speed reached, maximum weight lifted, and so on? In the past Marvel Comics and its mutant characters have attempted to do that with a decades-old classification system based on the Greek alphabet.
But until recently, this mutant classification system wasn't that formalized within Marvel comic book continuity. Sometimes 'Alpha' was used to denote the most powerful of mutants, while at other times 'Omega' was the most powerful classification. Nevertheless, versions of the system were used by the X-Men, SHIELD, the Shi'ar Empire, and others.
Recently, a more defined and official system was introduced in 2019 during the X-Men's 'Dawn of X' era, primarily focused on classifying the most powerful mutants in the modern Krakoan era - what is now officially called Omega level mutants.
"A mutant whose dominant power is deemed to register -- or reach -- an undefinable upper limit of that power's specific classification," reads a data page in House of X #1.
The new classification terms are for specific mutant powers, meaning a mutant with multiple powers could have an Omega-level power but also possess different powers at lower/different levels. For example, Jean Grey is an Omega-level telepath but her telekinesis powers qualifies at a lower level - meaning she is an Omega-level mutant, even if not all of her powers are at an Omega level.
Given the classification system is relatively new and a little bit complex, Newsarama breaks down the major mutant power classification categories for you:
X-Men mutant classification - Epsilon level
Mutant powers classified as 'Epsilon' are on the lowest end of the mutant power spectrum. These are traditionally non-combative powers - in some cases, it's a physical mutation that doesn't involve a special ability, but in others, it's a non-assuming power with no major effective use.
An example of an Epsilon-level mutant would be someone like Artie Maddicks, at least in terms of his physical mutation. His ability to project simple holograms has not been formally classified.
X-Men mutant classification - Beta level
The next level is 'Beta.' A 'Beta' level power has some practical application (as opposed to the lower, Epsilon level), but is generally minimally useful.
Rogue's early days as a villain, during which she absorbed the memories and powers of Carol Danvers (then Ms. Marvel) would be a good example of a portrayal of Beta-level mutant abilities.
For many years, Rogue didn't have control of her ability to absorb the powers and memories of others, leading her to harm other people as well as herself.
X-Men mutant classification - Alpha level
'Alpha' level mutant powers are the most common superhuman abilities - at least in terms of what readers of Marvel's mutant titles are most familiar with. They have applicable uses and the mutants who possess them to have the ability to control those powers within reasonable limits.
A good example of an Alpha-level mutant would be Cyclops, with his ability to emit beams of energy from his eyes.
Rogue, who we mentioned was initially classified as a Beta-level mutant early on, gradually learned to use her abilities - and after the events of the story X-Men: Messiah Complex, could control them to the extent that she was reclassified as an Alpha-level mutant.
X-Men mutant classification - Omega level
Omega level mutants are the upper limits of their categories in terms of mutant powers. So how does a mutant become defined as 'Omega' level?
Marvel uses Magneto and Forge to illustrate the difference.
Again, from House of X #1:
"Both Magneto and Forge are the most powerful mutants of their power types on the planet Earth (magnetism and technopathy, respectively)," reads the data page. "But what makes Magneto, and not Forge, an Omega level mutant is that the upper limit of Forge's measurable powers could hypothetically be surpassed (and, in fact, has by multiple humans on the planet), while the upper limit of Magneto's powers cannot be surpassed in any measurable fashion."
(Forge is an Alpha-level technopath.)
There can be multiple Omega level mutants for one power type, however. An example would be Jean Grey and Quentin Quire, who both qualify as Omega-level telepaths.
(If another name is popping into your head right now, read on…)
According to present X-Men continuity, there are currently 25 Omega level mutants: Monarch, Iceman, Elixir, Jean Grey, Legion, Magneto, Proteus, Mister M, Storm, Exodus, Quentin Quire, Vulcan, Hope Summers, and the recently-introduced Krakoan mutants Isca the Unbeaten, Tarn the Uncaring, Idyl, Genesis, Redroot, the Witness, Stulgid, Lodus Logos, the Knower, Sobunar of the Depths, and Xilo the First Defender.
It's possible for a non-Omega level mutant to 'graduate' to this level. Iceman's abilities/power levels grew naturally over time. Additionally, mutants whose powers are artificially augmented, such as when Cable's telekinesis was enhanced by Blaquemsith and Stryfe in Cable and X-Force #14, can also graduate to 'Omega' level.
If there's a mutant you might assume is missing from this list, you wouldn't be alone or necessarily mistaken. Curiously, the House of X #1 list of Omega level mutants - 'written' by Charles Xavier - does not include Xavier and his telepathy, which is conspicuous by its absence.
But this is the X-Men's official in-story list of Omega mutants for now. It's possible Marvel/Xavier hasn't yet accounted for all potential Omegas, or perhaps for in-story reasons he (and Marvel) are holding onto some secrets, which would be typical of Xavier. For example, Moira MacTaggert, who was recently revealed to have the mutant ability of reincarnation and has recently been described as uber-powerful, also isn't on the list.
Remember, this is comic books, so Marvel's mutant classification can, and almost certainly will change over time.
If you've made it this far, you're definitely an X-Men fan so make sure you've read all of the best X-Men comics of all time.