You arrive in the last corridor, after annihilating EVERY single monster in the underground. Except... Them.

Papyrus: "SO... YOU FINALLY ARRIVED..."

Papyrus steps forwards, his eyelight glowing a brighter shade of orange, as a long bone manifests into his right hand. A second skeleton steps out from behind Papyrus, one you recognised as Sans, who's eyelight glows a bright shade of blue.

Swap Sans: "I once believed in you... But... Seeing after what you done... I just can't."

A 3rd figure steps out from the other two, Asriel wipes tears from his eyes before dual blades materialises into his hands. Asriel's eye glows a threatening shade of green.

Storyshift Asriel: "I'm... Not going to be sorry for this."

All 3: "Let us teach you a lesson!"