Originally an orchestral work, the piano reduction of Respighi's Belfagor overture is a demanding virtuoso showpiece. It utilizes dense, late-romantic textures and requires significant technical stamina.
The technical hurdle is managing the large, rapid octave passages while maintaining structural clarity.
Comparable difficulty and character — good candidates for what to learn next.
Belfagor is rated Henle level 7 of 9 — late advanced repertoire, roughly ABRSM grade 8 and above. In the RCM system it corresponds to about level 10.
You should be comfortable at Henle level 7 — meaning you can already play level 6–7 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Belfagor lasts about 8 minutes.
Belfagor is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Wanderer Fantasy in C major by Franz Schubert, Toccata in D minor by Sergei Prokofiev, Rhapsodie espagnole by Franz Liszt — see the full similar-pieces list on this page.