ACTUALLY NEVERMIND I WOULD LIKE TO CANCEL MY PREVIOUS SUBMISSION.
I just found out that Castlevania: Harmony of Dissonance's ost counts as chiptune. So it's eligible.
Castlevania Harmony of Dissonance: Luminous Caverns
On paper, this theme sounds really repetitive and boring. But in context, the song plays in one of the most confusing areas of the game, which is an underground cave with a creepy atmosphere and the much more terrifying in appearance than gameplay Scarecrows (Those things freaked me the hell out when I first played the game. This is a place designed to drive you insane, and I love that they did it so perfectly, and the theme sells this feeling down to the note. But it's not the only theme I'll mention here.
Castlevania Harmony of Dissonance: Into the Demonic Castle
This is also another great song in the game. After using the Warp room, you find yourself in a strange place and nothing is quite as it was before. The backgrounds are also really weird, with... Volcanoes (?) in the background, misty clouds indoors, and crystals even. There's a sense of urgency with this song that tells you that you need to go forward. Not to mention that the song in on itself is pretty nice to listen to.
HoD's ost often gets crap for being 8-bit on a GBA game but I think that with the depressing tone the game takes, this is a very welcome accident. Everything sounds depressing and I love it, specifically these two themes.
Also this means that I've gone three days without FE now.