The way I would do infinite mode is:
- After level 16, you go back to level 1. You could replace the final boss with an ordinary Area 4 level.
- You lose all your items, except for bombs, ropes, HPs, and Kapala.
- You can visit the Black Market and CoG again.
- All monsters have double HP.
- After level 32, now all monsters have triple HP. (etc)
If you want to be really nasty, have more dark levels. Have some dark levels where the player isn't given a crate of flares.
I like this idea. I still reckon that a more fully random mode would be better but this sound a helluva lot easier to code.