This is copy paste from anonymous user so it's thread instead of talk page edit:
I've discovered that:
- In Normal difficulty, FPS is 15.
- In Hard mode, FPS may reach 21.
- In Easy mode, FPS goes down to 12.5.
- Swimming sections have half FPS.
- Cutscenes can have very different FPS values. For instance, when the friend throws the player over a gap, it goes to around 20 FPS.
- The end cutscene can go as low as 2 FPS.
- Windowed mode or fullscreen make no difference on FPS.
Some video proof: https://www.youtube.com/watch?v=0heCdJk_oU4 (sorry about the low quality)
These findings make sense, as the game data instructs the game VM how long each frame should be displayed. This means, essentially, that the game runs at a varying FPS, and runs on modern computers at the same FPS as originally designed.