Board Thread:General Discussion/@comment-26980570-20160320192450/@comment-26887879-20160906231736

Sans' lab seems to be resetproof, since there can be a picture of you and everyone from the previous pacifist timeline. There is a theory that Gaster's experiments didn't destroy only his life, but the whole timeline he lived in and Sans (and probably Papyrus) are the only survivors. That might explain why Sans so desperately tries to "go back".

Also, in that theory, Sans' lab is only thing remaining from that timeline. Blueprints we find in it might be Gaster's blueprints for CORE, that's why CORE exists in our timeline despite Gaster not being there.

Gray NPC, Mysteryman and Gray room might be scattered pieces of timeline Gaster was in and he destroyed.