Use arrow keys to move the heart, dodge everything! The HP Bar is a bit messed up, but you will die upon the 9th time you are hit by Sans bones! Basically, you will go through the yellow HP Bar in the game 3 times. This is like MajesticPie's "Undertale Boss Fight" game, but Papyrus-themed with more attacks that are more difficult to dodge, thus why you have more HP.
starting a new underswap boss fights
