1º idea
It would make the soul not attack you, but when a level 3 or 4 item appears, the ghost uses a die that lowers the level to level 2 or 1 and every x room the effect of the item is activated that can eliminate coins keys etc.

2º idea
You have a damage decrease but instead it gives you speed and you cannot transform into a ghost when you die.

you have an object 1 per floor eliminate all the hearts and you are left with half a red heart or 1 red heart and that floor the ghost does not attack you the item would be called something like: suffering

3rd idea
When he repents of his sins he still has hallucinations of all the suffering of the victim who still cannot rest he wants to torment you even more

Now several ghosts of enemies that you have already killed will appear randomly in each room, but with half life but double damage.

You will no longer be able to obtain white, blue or black hearts in any way. Red hearts will only appear as half a heart. There will be no items that resurrect you when you die. You will not be able to find a Genesis death certificate and you will not be able to access the angel room. The demon rooms when you pick up. One of its items gives you broken hearts and will increase the ghost's speed and damage.