Item Duplication
Item duplication, or duping, allows you to create permanent duplicates of any item in the game, from the Kings Sword of the Heavens to stacks of gold.
In order to duplicate items, first make sure that there is room in your inventory for the item you want to duplicate. Now drop the original item on the ground and close your inventory. Ensure that you have at least one usable item on your belt. Walk away from the item to be duplicated. The distance you should walk away depends entirely on how quickly you think you can bring your cursor to your belt.
Now, click on your item as if to pick it up. Right when your character is about to pick the item up, left-click on any item on your belt. The item will have been picked up but you will still be holding the item from your belt with the cursor. Drop that item on the ground and it will be the duplicate of the item now in your inventory.
Item duplication is most easily accomplished in games with no lag.
God-Mode
In order to use this God-Mode cheat, you will first need some sort of armor that grants you health. The more health your armor gives you, the easier this cheat will be to pull off. You will also need the Mana Shield and Blood Star spells.
First, cast Blood Star and drain your life as low as you can without killing yourself. Now cast Mana Shield and remove your life-giving armor. Your hit points should now read zero and you will be invulnerable.
Just remember to put your life-giving armor back on before leaving the level you are presently on, otherwise you will arrive on the other side of the staircase or town portal dead.
Stealth Mode
In order to make yourself invisible to monsters in Hell and the Caves, use enough light-radius reducing equipment so that you have a light radius of -80 percent. Now the monsters inhabiting these areas will be unable to see the light you give off. You will have also have a hard time seeing them, but this can be rectified by using Infravision spells or scrolls to reveal monsters and holybolts to illuminate walls.