I am returning to working on the fangame now, and to kick off I will be showing the idea I have planned for phase 4.

Firstly, Phase 4 will be one of the most difficult phases with Sans using the power of DETERMINATION and other soul traits inside his body. KR will be present but DETERMINATION attacks will ignore KR and deal HP damage instead. (Sans has the power to use DETERMINATION due to phase 3 sans having a large amount of it already.) The two attacks in the video aren't the only ones.

Secondly, to advance in this phase, Sans will have to be attacked as he is using another soul trait other than DETERMINATION in order to destroy that trait and prevent it from being used again. Then after all traits (Excluding DETERMINATION) have been destroyed, Sans can be attacked directly. After that, Sans has to reach a low health amount to trigger the 'The End' Cutscene.

Feel free to give me opinions on the idea for the phase.