During the game push F10 KEY where KEY is: G - Unlimited strength I - For more light W - Level jump Z - Stop time and monsters
Delete, rename or move the LIGHTS.DAT file in the DATA folder to make all the dark places become bright.
Repeatedly throw a potion or scroll against a wall (or just send a Fireball at it if you're impatient) until the item turns in a pile of debris. It would seem to be a wasted, but when you pick it up, you'll find that you can use it infinitely. Get one of Heal, Fly, Restore Mana, Light, and Smite Foe, and you're nearly invincible.