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Dark Bum converts useless Red Hearts into Black Hearts and Spiders. Mitre and Daemon's Tail replace useless Red Hearts with Soul and Black Hearts respectively. Crown of Light will always activate when entering a room, but still deactivates after taking damage.
Like Abaddon, this item is always safe to take.
Ceremonial Robes costs three Soul Hearts and grants three Black Hearts and damage up. Book of Revelations Spawns soul hearts. The XI - Strength card gives ? a permanent soul heart.
The Rune of Dagaz grants one soul heart as well as lifting any curses. Balls of Steel pills or V - The Hierophant grant two soul hearts, both of which are more useful than normal HP up items. Athame can be used to produce black hearts upon taking damage. Abaddon will give 2 black hearts on pickup, granting its effects essentially for one heart. Abaddon can be bought safely regardless of current health, because its price can be deducted from the acquired Black Hearts retroactively. Abaddon costs three Soul Hearts and grants six Black Hearts, damage up, fear shot, and no negative effects to ?. Health down pills will remove 2 soul hearts instead of 1, however. Birthright: Soul hearts gained from health ups will be doubled. Bone Hearts grant an empty Bone Heart upon pickup, but they cannot be refilled using Red Hearts. Furthermore, in rooms with non-flying enemies that chase the player (except Spiders), the poop can be used in a corner of the room making ? untouchable, allowing the player to kill them without taking damage (if the player moves away from the pile of Poop generated, this will no longer work). The Poop - While not the most useful item, it can allow ? to cross small gaps by bombing the Poop from the opposite side, much like one would for Rocks. Enemies who deal full hearts of damage can be very dangerous in the early floors of the game. Sleeping on a bed will give ? three Soul Hearts.