Binding Mask (5e Equipment)
From D&D Wiki
Wondrous Item (Mask), Very Rare
This rounded mask, made up of a polished slab of some unknown substance, is a ruddy color akin to a plum, with faded teal tentacle-like whorls decorating the outer edge. In combination with the trio of red orbs, set into the center of the mask as the only objects that project from its smooth surface, the visage it portrays resembles the face of an aboleth. Indeed, it was the aboleths who sculpted the first of these relics from the stuff that lies upon the intersections of the ocean's depths and nexuses of otherworldly energy, and harnessed the potential within them to shape the erratic stuff of its magical signature into aught that would compel the service of the servants they believed they were owed, up on the surface world... and hasten a return to an age of the deep, in which they rule once more.
While worn, this magical item provides its wearer the following benefits:
Curse - Thrall to the Depths
However, the truth behind these boons is far more sinister- preparation for the creation of an ideal vassal. Upon initially donning the item, once attuned to it, something about the item seems "unusual". The wearer may make (in secret) a Wisdom (Insight) Check against a DC of 20; on a success, they intuit that there is more to the mask's effects than initially seems the case, and that it would be a good idea to not wear it until its full power is known.
At any rate, if worn for 1 hour by an attuned, it becomes impossible to remove from the wearer's face by mundane means- a Remove Curse spell (or Wish, used to replicate Remove Curse) is required to detach it.
Once the bearer takes a Long Rest with the mask so attached, its edges merge seamlessly with its wearer's own face, and the curse fully sets in. After a set number of days thereafter, as indicated, each of the following set in. These effects, should the mask be removed with Remove Curse or similar magic prior to Day 7 (see below), require a Heal spell, or another disease-curing spell cast at 6th level or higher, to cure.
The wearer gains Vulnerability to Psychic damage, but Resistance to Acid and Cold damage. In addition, a series of long, prehensile tentacles, each roughly the length of their leg, grow from their back (likely damaging or destroying any armor or clothing items worn while the wearer was asleep; this falls to the GM's discretion.) While the wearer is obviously changed and more monstrous in nature in a way that cannot easily be hidden, and cannot wear any clothing or armor items over their torso not specifically made to accommodate the tentacles' presence, they do gain an additional tentacle Attack (1d6 bludgeoning) that they can either Attack with independently, or use a Bonus Action to Attack with as per an off-hand weapon.
The wearer's tentacles double in length, gaining Reach when used as a weapon. They also suffer a minor version of both the Aboleth's Slime ability:
The wearer's tentacles develop further- when used as a weapon, they may automatically initiate a Grapple on a successful Attack check with them. If the target is Medium or smaller, they are automatically Restrained for the duration of the Grapple- either way, the Tentacles cannot be used to Attack again until the Grapple ends. The wearer's curse also develops further, eroding their grip on reality- they suffer Disadvantage to Wisdom and Charisma Ability checks and Saving Throws, and feel a need to seek out the nearest ocean, lake, or other large body of water.
The wearer's mind finally breaks, and is subsumed by the mask- from then on, they devote their time to seeking out the ocean, or routes to it, in order to give themselves over to the masters that rule its depths (i.e. the aboleths.) The rest of their flesh, as well, begins to flush the same deep violet as the mask, and to begin sporting cyan tentacle-like whorls. At this point, the original character is gone, and nothing short of a Wish or divine intervention can undo the mask's fusion with and subsumption of the original wearer's spirit and flesh.