One of the big advantages of being a skeleton - and sadly lacking the impressive musculature he would surely have, if he had flesh - is being a much smaller target than his height implies. Bones are narrow enough, tricky to hit. At least as long as they're working without videogame rules; his hitbox would be easy to hit.

Papyrus flinches back, a dusty red bone spawning to block the incoming tail before he even realizes what's attacking him.

"Oh my god! Sans, what are you doing?" He exclaims, readying another tainted bone to hand. "Are you possessed?? I don't think anybody has berserker-inducing powers..."

His expression, his tone, they're almost normal of him. If it weren't for his new look, and the way he's using the Void powers for defense, instead of pinging one of them back with a blue attack... Would anybody be able to guess something's amiss?