Whilst it's for violin and piano rather than piano solo, try the middle movement of Alkan's Grand Duo Concertant Op. 21 with its giveaway title l'Enfer which, although dating from around 1840, sounds as though conceived in the 20th century and indeed its opening bears an uncanny resemblance to that of Busoni's Sonata No. 2 for violin and piano, albeit far more threateningly; also there's no. 45 of the same composer's 49 Esquisses Op. 63 which has the similarly giveaway title Les Diablotins which was first published about two decades after the Grand Duo but still inhabits the 20th rather than 19th century with its cluster chords (if you please!) that I've read described as "reminiscent of Ornstein, Ives or Cowell, or would be had they not predated the biths of all of those composers!"...
There's no shortage of other scary pieces by Alkan, even though some are just more scary to play than to listen to, not least a few that somehow almost feel as though they have to played too fast in order not to sound as though they're under tempo! (for example the Scherzo focoso Op. 24, the finale of the Symphonie that is no. 7 of Douze Études dans les tons mineurs Op. 39, the last of the three études Op. 76 nd indeed the finale of that Grand Duo, although there are others).
Best,
Alistair
Topic: Scary pieces