Chopin op 10/2. Double thirds, Double sixths... In fact all these etudes are stinky hard...especially to sound decent.
Mvmts 1 or three from Petroushka. 1st mvmt of petroushka is 2 minutes long and is hard to sound like pollini. Mvmt three is 6 minutes long and is JUST HARD to play all the notes as written.
Bartok Etudes....AHHHH!!!! But oh so cool.
of course feux follet...