Long ago, a Tiefling mage from the Arcane Brotherhood (a society of renegade wizards based in Luskan) came to Undermountain in search of forgotten knowledge. In his travels he found Dweomercore, an academy of magic designed to test, trap, and confound its students. After only a few months of enrolment, he was accused of spell theft and his association with the Arcane Brotherhood was revealed. As both a precaution and a warning, Halaster killed the mage and turned his heart into a magical trap. It's original purpose was to simply turn adventuring parties against each other, but a part of the mage's spirit still lives on within it, and now within you.

Hidden: Casting any spell which would reveal the nature of this item fails, instead only alluding to certain aspects or features.

Curse: This item is cursed. Upon attuning to this item your own heart is replaced by the Withered Heart, You gain all of the features listed below, and cannot un-attune. Your character is aware of these changes but sees no need to inform the other member's of the party, and does not wish for the curse to be lifted, actively avoiding any attempts to do so. The curse is broken when a Greater Restoration or similar spell is cast on you whist you original heart is within 5ft. Doing so replaces your heart once again, un-attuning you from this item, and ending all affects granted by it. Once the Withered Heart is removed in this manner, it is engulfed in radiant light and is destroyed.

A Change of Heart: Your alignment becomes Neutral Evil. You also gain the bond "The Haunter of Dweomercore must die". Upon the Haunter's death, your alignment returns to normal and the curse on this item is lifted. You retain all features of the Asmodean Inheritance trait, although if your original heart is still in your possession, you may spend a short rest un-attuning from the item, after which all affects are undone. The Withered Heart is not destroyed if removed this way, and re-attuning does not apply the Curse, Bound Soul,or the A Change of Heart features.

Bound Soul: The spirit of the mage has grown accustomed to "life" in Undermountain. While you are Cursed by this item, you cannot willingly leave Undermountain, if forced out by any means, such as a charm spell, your most important goal is to return there. The magical nature of Undermountain also sustains the mage's spirit. If you spend more than 1 hour outside of Undermountain, this magic ceases to function, your heart stops, and you die.

Asmodean Inheritance: The demonic nature of the heart's previous owner grants you the following benefits:
     Darkvision: You can see in dim light within 60 feet of you as if it were bright light, and in darkness as if it were dim light. You can’t discern color in darkness, only shades of gray. If you already have Darkvision, this feature instead extends it by 60ft       
     Hellish Resistance: You have resistance to fire damage.
     Infernal Legacy: You learn the Thaumaturgy cantrip and can cast the Hellish Rebuke spell once with this trait and regain the ability to do so when you finish a long rest.
     Devil's Tongue: You can speak, read, and write Infernal
     Appearance: You gain 1d4 + 1 of the following physical traits. Roll a d12 to determine which ones are applied, re-rolling duplicates or any which would clash with your existing traits (e.g. Dragonborn with Scaly Skin)
          1. Small Horns
          2. Fangs or Sharp Teeth
          3. A Forked Tongue
          4. Catlike Eyes
          5. Six Fingers on Each Hand
          6. Goat-Like Legs
          7. Cloven Hooves
          8. A Forked Tail
          9. Leathery or Scaly Skin
          10. Red or Purple Skin
          11. Cast No Shadow or Reflection
          12. Exude a Smell of Brimstone

Notes: Sense: Darkvision, Resistance: Fire, Language: Infernal, creature with a heart