Source: Eberron - Rising from the Last War

Armor (any), very rare (requires attunement)

This hideous armor is formed from black chitin, beneath which veins pulse and red sinews glisten. To attune to this item, you must wear it for the entire attunement period, during which tendrils on the inside burrow into you.

While wearing this armor, you have a +1 bonus to Armor Class, and you have resistance to the following damage types: necrotic, poison, and psychic.

Symbiotic Nature. The armor can't be removed from you while you're attuned to it, and you can't voluntarily end your attunement to it. If you're targeted by a spell that ends a curse, your attunement to the armor ends, and it detaches from you.

The armor requires fresh blood be fed to it. Immediately after you finish any long rest, you must either feed half of your remaining Hit Dice to the armor (round up) or take 1 level of exhaustion.