It's definitely a bug, but it delivers absolutely new game expirience.
Prerequisites: Find potion of flame or fire seed. Go to nearest chasm.
Conditions: You staying right near the chasm. You burning. You have 1-3 HP. So on next step you will definitely die from fire.
Action: JUMP TO CHASM RIGHT NOW!
Result: You become alive ghost with 0 HP. But! You can move, you have 1 step sight area (so blindy). You always invisible for enemies. You can attack them with 100% accuracy without getting revealed. Literally you do not exist for monsters, they moves constantly away from you. Items cannot be used from backpack (all buttons disabled), but some of them like scrolls and potions are available through quick-slot. Using heal potion or dew vial or stepping on dew will bring you back to life to a normal state hero.
I completed three dungeons and two bosses in ghost state, Goo was easy, Tengu - takes much time to kill, but DM-300 cannot be killed - he constantly moves on heal plates.