Hey Mod Tem!Frisk here to explain what happened!
Disclaimer: It’s fiction so I can screw it up all I want.
The previous pageset to the huge mess of black and white, had a singular abnormal thing appear in the last page
Oh look at that weird black mass! Weird right? Totally!
What is it? Essentially a black hole. Created from what was extracted from Chara. You know, the same stuff that removed the floor.
So this thing blows up and absorbs the underground.
Papyrus(WingDings) is the closest to the machine and exposed to the largest amount of the energy and determination. So in the “void” he contains the most form and determination to survive, you know, in Papyrus style. Motivating the souls to survive.
The souls all joined up (Which was hard to express but I tried!) with Papyrus, he controls their mass and recreates his form (He became an algamate with all the souls that were dragged in.) when he reaches out for Chara’s soul in the “void”.
It might have had something to do with this
Also remember during Chara’s story when this happened?
Man, that was strange…