WARNING: The following contains spoilers for X-Men #7 by Gerry Duggan, Pepe Larraz, Marte Gracia, and VC's Clayton Cowles, now on sale from Marvel Comics
In the Marvel Universe, Omega-Level Mutants are considered the upper echelon in terms of mutant potential. They're among the Marvel Universe's most powerful beings, defined as mutants with no technical limitations in their powers.
Recent developments in X-Men have suggested Synch might quietly be an Omega-Level Mutant, capable of effectively calling upon any power as needed. If this means that the classification is being reconsidered for other mutants, however, there are a few others who deserve that same kind of recognition.
Polaris Might Outclass Magneto One Day
Polaris has recently been on an upswing in terms of recognition. She was a major figure in the Fox television series The Gifted, became a major member of X-Factor, and was elected to the X-Men in the first Hellfire Gala election. Along the way, she's shown off some incredible potential that might even allow her to one day surpass her father Magneto. Considering he's already considered an Omega-Level Mutant, this might mean she'll one day replace him in the pantheon of mutants.
The biggest difference between Magneto and Polaris in terms of power comes with Magneto's age. The experience he's gained and his ruthless nature means he's pushed his power to limits while Polaris just hasn't yet. But Polaris' powers have increasingly matched her father's. She recently even used her abilities to more or less casually create a static field that contained a nuclear plant's overloading core. She's held her own against Magneto one-on-one, and there's no reason to think she won't grow more powerful with age. While she might not be there yet, Polaris is likely on the fast track to becoming recognized as an Omega-Level Mutant.
Forge Can Build Anything And Everything Mutants Could Ever Need
Synch has copied many powers during his recent tenure among the X-Men, even Omega-Level powers like Jean Grey's telepathy. But while borrowing Forge's abilities, Synch made the comment that he believed Forge might be Krakoa's most powerful mutant. He's not wrong, either: Forge's ability to effectively build anything he can think of has been a vital attribute during the Krakoa Era. Forge has a wealth of knowledge, both technical and magical, that he can adapt for his inventions. In theory, his power is limitless in its creativity and potential.
The only reason Forge hasn't been considered an Omega-Level Mutant before this is that other genius inventors like Reed Richards and Tony Stark theoretically equal or surpass him. The definition of an Omega-Level Mutant is that no one else who shares that same ability can outclass you, so technically Forge might not be an Omega-Level Mutant. But at the end of the day, his powers are unique within the mutants so far introduced, and both Stark and Richards have been shown stumped in the past in ways Forge never has been. In practice, there's no reason Forge isn't considered an Omega-Level Mutant.
Blink's Teleportation Doesn't Slow Her Down At All
There are technically two versions of Blink currently in the core-Marvel Universe, the Earth-616 incarnation of Clarice Ferguson, and her Age of Apocalypse counterpart who became a reality-hopping hero with the Exiles. It's the latter who's revealed just how powerful Blink is, with her teleporting powers lacking many of the constraints that hold back others. Capable of creating holes in space, Blink is effectively Marvel's most powerful teleporter. Notably, unlike other teleporters like Nightcrawler, using her powers doesn't ever seem to deplete her stamina.
Blink also has a unique number of ways she can use her powers offensively, deflecting attacks with ease or even teleporting part of a target away from the rest of it. She can also teleport numerous people at once through her portals without suffering physical exhaustion. It's this element that makes her potential truly unique. Blink's typical teleport limit is from the Earth to the Moon, but that could change over time. In theory, Blink could use her powers to create countless teleports with no apparent cap on her abilities. This means she's potentially limitless with her powers, making her technically an Omega-Level Mutant.