A highly polished version that closely replicates the original animation by FlamesAtGames. It features multiple phases and intense gameplay.
You can find the various versions on the Game Jolt Disbelief Papyrus Search Page.
In this AU, Sans tries to stop you in Snowdin instead of Papyrus, leading to his early death. This forces Papyrus to witness the loss of all his friends, eventually pushing him to lose his characteristic "belief" in your goodness. When you meet him in the Last Corridor, he wears Sans's jacket and wields powerful bone-based and soul-manipulation attacks.
A more accessible version for players who want to experience the story without the brutal difficulty of the original. Download Links:
The mod is typically played using or its successor, Create Your Frisk (CYF) , which are engines specifically designed for recreating Undertale-style battles. How to Download the Disbelief Papyrus Mod