I had wanted to take some screenshots of the game where the HUD is gone, and my character can't be seen (either because they are invisible or it's a first-person view). The ability to float around (a 'noclip' or 'fly' mode), and monsters not being able to see me (so I can observe them go about their routines) would be welcome as well.
But alas, any way of doing that remains a closely guarded secret.
I wasn't asking this for purposes of cheating, I don't have a problem with the challenge of the game, except after level 28 or so, and the problem there is that there IS no more of a challenge to the game, it really was for screenshots.