Horror Sans was a Sans from the neutral ending where all the main characters are alive, but some enemy encounters were dead causing Undyne took over. The CORE failed, causing a lack of magic, making alll sorts of horrible things happen. Sans was fine because his special eye was actually his soul and magic. Undyne and Alphys took his eye to power the Underground, but without destroying his eye he couldn’t die.
Horror Sans by Sour Apple Studio
