Play with what you have. Key seems to be D#m/Ebm. Drop C# is the best tuning to play this song "seriously" and I'd recommend it - though you lose a couple of notes if playing the low riff in A pt II.

You may notice there's often some dissonance in this song - many accidentals (notes not out of the key/scale) - particularly on the bass and the bass line is not very standard to say the least :)

This is the longest I've ever used to figure out a short song. Video game music is usually easy to transcribe and tab, but this piece is totally crazy. Kinda wish they build a bit more on the riffs because this would make really good as a longer version - this feels a bit "cut short" - especially Part D, that is very cool and only lasts for 4 bars. I guess video game composers gotta make 50 more songs asap, so songs don't always reach full potential.