This is a huge master post containing tons of lines of dialogue and all the proof and my logical interpretations of Sans. Here is the TL;DR. Sans is highly hinted at as being in a costume. He eats food that he can drink through the immobile teeth in his mask, eating more than monsters, he is always tired and sleepy, he can teleport, use magic, and has advanced powers, he may emit slime, he knows about humans, he once lived in a place different from the current surface world and gave up using the broken machine to go back, he is linked to science and some organization that monitors and protects timelines, he knows things only someone that has lived in human societies would know, he lacks any determination, he doesn’t have a visible human soul, he is trained to investigate and perceive timeline related changes and alternate universes despite not being able to save or reset or remember resets. Sans also has a connection to Gaster, and knows about determination.
He isn’t a skeleton, he isn’t a normal monster, and he isn’t a normal human.
want to know more or want evidence because youve got a bone to pick with my interpretations? read below!