Warning: Spoilers for X-Men Infinity Comic #35 ahead!
One of Krakoa's most powerful mutants of all time, the telepathic Jean Grey, has just been confirmed as the X-Men's heaviest hitter in the pages of the X-Men Infinity Comic #32. The Omega-level mutant has not only near-infinite power, but also the rare ability to actually control it, making her the X-Men's best "closer."
Jean Grey has one of the more complicated X-Men backstories, dying and being resurrected many times, mainly because of her otherworldly cosmic connection to the Phoenix Force, the power of "life incarnate," which greatly increased her abilities in the 1980s. In fact Jean Grey, or Marvel Girl as she is sometimes called, is so incredibly overpowered that recent writers at Marvel have nerfed her abilities a bit, making her more aligned power-wise with other members of the X-Men, to keep her and their stories interesting.
The new X-Men Infinity Comic #35 - written by Alex Paknadel with art by Julian Shaw and Dono Sanchez-Almara - follows the mutant Maggott, a rarely utilized but fascinating character, as he tags along on an official X-Men mission, apparently as back up and clean up crew. Japheth, whose ability manifested in him having two techno-organic slugs, Eany and Meany, in his stomach that can eat anything, is watching on as the X-Men battle what appears to be a human-turned-sludge monster whose touch decays anything. All of the X-Men are failing to destroy the monster, with Polaris and Rogue failing epically and Wolverine having half of her flesh horribly decayed. Finally, Jean Grey steps up, which prompts Maggott to say, "You want a show, you bring Gambit or Illyana... but if you want an actual closer... there's only one of us who can bring home the win every single time without fail." Of course, Jean Grey's destruction of the monster is not entirely without fail, as it manages to revive itself briefly to consume and kill Japheth before it is fully put down.
An Omega-level mutant is a mutant whose upper limits of their powers have never been, or are unable to be, recorded, meaning Jean's potential power is currently seen as infinite and limitless. That being said, just because a mutant is Omega-level does not mean that they are automatically a "closer," either because their power is potentially situational like Iceman's, or because they may have an internal or external barrier preventing them from utilizing their full Omega-level strength, like Storm and her claustrophobia. Jean Grey however doesn't really seem to have any internal barrier to her upper-level power, finally learning how to fully control all her abilities after rejecting the Phoenix for the seemingly last time in 2017's Phoenix Resurrection. While some stories are showing Jean's powers being "nerfed" it is clear that on the current X-Men team she is their closer, the one who can definitively end any battle without very much effort at all.
Jean Grey was Charles Xavier's first official X-Student, and her psionic strength is known throughout the cosmos, earning her the respect of all her peers and enemies. The X-Men have a lot of powerful members, but it's clear that Maggott and many other mutants on Krakoa view Jean Grey as their heaviest hitter, the one who can always take down the enemy.
X-Men Infinity Comic #35 is available now on Marvel Unlimited.