Start the game with: PRINCE MEGAHIT [Enter]
(In version 1.3 use IMPROVED)
This gives you access to these cheat keys:

[U] View screen above
[H] View screen to the left
[J] View screen to the right
[N] View screen below
[Shift]+[I] Inverts the screen
[Shift]+[B] Blanks out non-animated objects
[Shift]+[W] Float down
[Shift]+[S] Heal a health point
[Shift]+[T] Add a health point
[Shift]+[L] Advance to the next level
[+] Increase time
[-] Decrease time
[K] Kill the guard you are fighting