The Dark One's Tattoo

Alter: As an action, you can speak the tattoo’s command word, hexing yourself. While hexed in this way, you take 1d6 necrotic damage whenever you hit a creature with an attack for the next minute. The target of your attack takes necrotic damage equal to three times the necrotic damage your received from this hex. Once used, this tattoo can’t be used again until you finish a short or long rest.
Each time this tattoo’s effect is activated, it grows in size. Once the tattoo threatens to consume the bearer's entire torso, they tend to disappear.

Attunement: Yes. This tattoo is cursed. Attuning to it curses you until you are targeted by a remove curse spell or similar magic. As long as you remain cursed, you cannot unattune from the tattoo. Once unattuned, the bearer takes 10d10 necrotic damage, this cannot be reduced in any way.

Materials/cost: 405gp
Placement: Torso
Rarity: Rare
Produced by a special needle, this magic tattoo symbolizes darkness and corruption.

There was once a very unlucky tattooist who witnessed an otherworldly monster viciously drain the life force out of one of his companions in front of his very eyes. Thankfully, the being vanished immediately afterwards, but this moment haunted the artist for the rest of his life. On his deathbed, he finally sketched out a design that had been fixed in his mind since that terrifying encounter.