I've posted so many Megalovania covers at this point one might think seeing the real word "Megalomania" as the title of a song was a spelling error when it's posted here.
It isn't, though.
This song's title probably inspired Megalovania's title (and at one time was apparently intended to be used where Megalovania was first used, in an old game hack).
It's funny because I actually stumbled on it completely independently of the Undertale fandom. (The video linked here introduced me to it slightly indirectly.)