I don't exactly know what the item would be perse, but the concept is an item that would be gotten through a Deal with the Devil, or through Chaos, should you collect that on a run.

The function would be similar to the item Damocles, but how it would work, is that upon collection of the aforementioned item, you would claim a MASSIVE stat boost across the board, (Speed would immediately be capped out to the max, and all other states would get a 5 buff, with an additional heart container granted upon pick-up) BUT the trade off would be that every room complete would have a 7.5% chance to take away a full heart off of you, stopping at the final heart, so it doesn't outright kill you. This would not remove the actual heart container in question, but would deal damage to you in a manner that would not affect your chances at further subsequent deals in the future (such as sacrifice rooms, or cursed rooms).

Perhaps it could even alter your attacks to be similar to the robed tentacle melee enemies you find in the later stages of the alternative path to fight the new "true" final boss.

I dunno. It's just an idea I had while playing a few days ago. It might also already be a thing in the game too.

Sorry if this ends up being trashed, or labeled as spam. I don't mean to cause any problems within the subreddit.