Most of the W.D. Gaster remixes I find around the internet have either sort of tragically heroic vibe or are creepy and ominous (presumably meant to set the tone for fighting him during a No Mercy and Pacifist playthrough, respectively). I always thought that since he's scattered across space and time or whatever, he'd be present in all possible timelines, and thus the fight would incorporate elements from both ends of the spectrum. This is my attempt (and kind of horrible failure) to combine both the creepy and heroic interpretations of Gaster's character. 

For those curious, cacodemonomania is the belief that one is possessed by some sort of demon or other malevolent spirit. Thanks, Wikipedia!

This song incorporates elements of Gaster's theme, Core, and a little Megalovania, since leitmotifs are very much a thing in the original soundtrack. 

Speaking of the original soundtrack, Undertale and all its music and characters (including the aforementioned tracks and characters) belong to Toby Fox, I mean no legal harm, etc, etc. I did make the image though c:

Cacodemonovania (minor Undertale spoilers)

exetior sans sonic exe ivan electro killer arhi demon dragon megalodon

Cacodemonovania (minor Undertale spoilers)

Deus Zed Machina