For good double features or pleasant sequences of multiple films in a row—so I don't have to keep making a new Swanychrist Challenge every time I want to recommend something.

1. The Swanychrist Challenge (1 to 5): Black Swan >> Irréversible >> Antichrist >> Bonus/Aftercare: Frontier(s) or Melancholia
2. Evil Sadly Lurks (6 to 7): When Evil Lurks >> The Sadness
3. Demon Eyes Æternal (8 to 9): Starry Eyes >> Neon Demon >> Lux Æterna (bonus film)
4: (11 to 14) The Demoni series: Demoni 1 and 2 (Bava) followed by La Chiesa and La Setta (Soavi)

Let me know if you try any of these out! They are experiences.