WARNING: The following contains spoilers for Marauders #26, on sale now from Marvel Comics.
The mutant Bobby Drake (aka Iceman) has risen in his estimation of himself and the world over the years, with his original basic powers slowly being expanded upon to the point where the founding X-Man has discovered his true place among the Marvel Universe's most powerful figures.
A sudden battle (and easy victory) in Marauders #26 (by Gerry Duggan, Matteo Lolli, Rain Beredo & VC's Cory Petit) proves just how monumentally powerful Iceman has become, and teases a potential to grow even more powerful down the line.
Iceman is an Omega-Level Mutant. Although he initially believed his mutant abilities were limited when he was younger, his control over temperatures and ability to reshape molecules (including his own) while in ice form has granted him a number of uncanny abilities. Theoretically immortal due to his ability to create a new body as needed, Iceman has been called upon to use his powers for the betterment of Krakoa. This has included stepping up and being a part of Magneto's hand-picked team to terraform Mars into the planet Arakko, and in Marauders #26 that means taking on a threat single-handily that is known for felling entire superhero teams.
While transporting Krakoan alcohol across the sea, the Marauders are set upon by Fing Fang Foom. The massive monster, returning from an intergalactic fighting tournament, seeks to steal the alcohol for himself. But Iceman, still comprehending the sheer extent of his powers, throws himself into a fight with the massive dragon. The Omega-Level mutant lands a couple of good blasts on Fing Fang Foom before the massive dragon shatters his body. At that point, Iceman simply creates a new massive body closer to Fing Fang Foom's size, and proceeds to fistfight a dragon. He proceeds to beat down the reptilian Thor villain, even reconstituting his body after being bombarded with flames and using the remnant ice pieces of his broken body as projectile weapons.
Ultimately, Fing Fang Foom retreats, as the mutant taunts him about respecting his power. On top of all that, Iceman isn't even exhausted afterward. Whereas groups like the Avengers have had to scramble to placate and contain Fing Fang Foom, the founding X-Man is so amped up after the fight that he can't even return to his normal form, so he decides to remain a giant and simply walk back to Krakoa from their current place in the middle of the sea. It's an incredibly impressive showing from the mutant, and a good reminder to both his allies (who are shocked by this display of power) and his sudden foe how powerful Iceman really is. So long as there's water nearby, this powerful mutant has proven to be more or less unstoppable.
While the definition of Omega-Level Mutants makes it difficult to parse out exactly who is the strongest, Iceman might have a good case for being at least the most physically impressive of the bunch. His ability to create new bodies mid-battle without any apparent distraction speaks to his sheer capability and allows him to more or less respond to any threat with a new body at his command. He could theoretically be considered on an entirely different level than almost any other Marvel hero, as he can force the retreat of an enemy who has given Asgardian Gods trouble in the past. Considering his relative youth, it's only reasonable to assume Iceman will become more powerful as time wanes on, possibly surpassing his current status eventually.