The sans is Ness theory is: sans is Ness from Earthbound. There is evidence to support this theory. The first piece of evidence is the room that you unlock in the Last Corridor. The room is sans's room which has a key to the back of the house. To unlock the room you have to open and close the game several times and keep talking to sans and don't save. To watch a video on it the link is https://www.youtube.com/watch?v=T5oBdbQ-eew. The back room has a picture of sans with people you don't recognize, along with a broken machine, blueprints and a badge. The badge could be the Franklin Badge, the broken machine could be a time machine, and the picture of sans with the people you don't recognize could be a picture of Ness and the people in Earthbound. A lot of people believe that sans once was Ness and then appeared in the Underground mysteriously. In the game when you talk to the Snowdin Shopkeeper she says sans and Papyrus just appeared randomly. The link to see the Snowdin Shopkeeper talking about that is https://www.youtube.com/watch?v=3wMOA4IpNko. Papyrus's costume has a symbol on it which resembles Starman from Earthbound.
This was it for the sans is Ness theory. Thanks for reading!
A video on this theory is: https://www.youtube.com/watch?v=KYdDUXyFocY.
There are many more videos on it on YouTube.
Remember this is just a theory and I didn't make it up. It could be true and it couldn't be true.
