I completly understand on why you get confused, because I am bad at explaining things, but Ill try my best anyway.

The key difference is this:

Dust!sans has to break his morals and do something bad for the greater good

Megalomania!sans dosent have morals and does something bad for the sake of doing something bad.

Dust feels bad about killing everyone. Megalomania doesent, in fact he enjoys it, "because ist only a game".

I could in fact execute this idea without sans killing anyone.

#Undertale #UndertaleAu #Fangame #Sans #UNDERTALEUpsideDown #UUD