Sans was a teleported to the lost episode, he was lost a nowhere to seen papyrus, Takwa was killed a lot of victims, Adam appear it.

When sans trying to kill it, she possessed or some point, he begin to eradicate all human victims all around the country.

Marcel was hiding the closet for months and Sans appeared and gone insane, he shapeshift to an evil twin realized finally he snapped.

He has a bone magic, mimic corpse, teleportation, shapeshift, he's using a gaster blaster in this point and he can teleport their closets to found him.

You need to defeat him and need to get out of the episode as soon as trying to break in.

@takwathefniamouse