It takes a second to reorient himself after they move, and Papyrus shifts the bones to provide whatever loose cover they can while Sans and Carly discuss strategy... and he considers one of his hands, the metal now likely permanently covering it, and some of the comments that not-Sans had been making, before.

"That sounds about right... and, I distinctly remember swords, in the instructions. You were asleep for that," he tells Sans, "but I think they mean to attack her core, once we can reach it. So, maybe we fight blasts with blasts."

He doesn't bother with showmanship, just letting a fanged blaster form several feet above his head and fire off a beam of crackling white light at the Mother of Invention's torso.