Not that it's the most demonic peice out there, but everytime I think of it the first adj that comes to mind is demonic, added together with the fact that I've been talking about it for a couple of days now, I'll throw in Chopin's 3rd Scherzo in C#min for its opening, octave sections (up to main theme), and Coda.
Demonic isn't the foremost adj but it is certainly there, wicked is much better but still not it. I don't even know if there is a word that can capture all of the characteristics; morbid, demonic, chilling, & the downright state of rotting well enough to describe the impact that the peice which bears the most ironic name borrowed from it's time signature...Vivace - Movement IV from Sonata No 2 in B flat minor by Chopin. "Wind over Graves" just bearly scratches the surface. I would add disorienting to the list of adjvs.