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I do wish there was a more polished-sounding version of the Halloween Hack Megalovania (besides the Homestuck one, which, while good, only uses the original as an overshadowed-by-guitar base).
I really like the progression of the original, and while the Undertale version's good, the original definitely feels more like the name.
I also feel like the Cognative Dissonance version (while completely unauthorized) is a really good take on the same progression, it needs a bit of cleaning up in places, just in general.
In short, Megalovania is just really good.

But, I also invoke the existence of Gadobadorrer, which absolutely rocks in itself (and the composers behind "Undertale: The Halloween Hack" recognized that too, with two covers of it that mix Megalovania in alongside other Brandish motifs: "Kill the Monster" and the updated version, "THE DARK REVENANT", named after the remake of the first Brandish, released on PSP).

I feel like I've gone on a tangent, but... oh well.

halloween hack megalovania > undertale megalovania

Synchronicity being taken basically directly from Brandish 2 lends more credibility to the theory that Megalovania was inspired by Gadobadorrer from the same game.
Considering the protagonist is Varik/Ares from Brandish, that only makes it even more likely.