Issue #157. Kitty scares the pants off the Shi'ar forces attacking Earth by disguising herself as Dark Phoenix reborn - and her only display of power is phasing up through the floor!note And this was well before Jean's first actual resurrection...
Issue #11. 'All of it. But special mention goes to Fabio and Magneto.
Fabio gains control of his power to fire off his gold balls in a straight stream that blows the Blockbuster Sentinel off its feet while announcing his mutant name: GOLDBALLS!
Then Magneto shows up, broken powers and all, and takes out the adaptive Sentinel by forcing hundreds of nails into it and then taking it out by having them tear out of it
Issue #16 is all Magneto showing he's a man of standards and still packing enough of a punch to be a force to be reckoned with.
Issue #19 has the team's known mutant powers being cut off or out of control. Tempus still manages to create a time bubble to save the team by shunting them forward in time by a minute. Magik, on the other hand, uses her sorcerer powers to utterly demolish the sentinels.
From Disassembled (2018 series)
In issue #1, X-23 takes out the entire Mutant Liberation Front single-handedly (with a magnetic Fastball Special assist from Polaris).
She tops that in the very next issue...getting swallowed by a T. rex and cutting her way out.