Oni Mask

Wondrous item, legendary, requires specific attunement process

A mask that is left behind once an oni falls in battle. When attuned and worn, the mask provides the following benefits:

The mask shapeshifts to fit your face.

When worn, the mask can be either visible or invisible. You can switch visibility as a free action. An invisible mask can be seen with truesight.

The oni's silver tongue is now yours. You have advantage on Charisma (Deception) checks.

Your frightening aura and visage gives you advantage on Charisma (Intimidation) checks.

The regenerative abilities of the oni are bestowed upon you. You regain 1d6 hit points at the start of your turn if you have at least 1 hit point.

Removing the Mask

When attuned, the mask can be removed by the wearer at will. However, when unattuned, the mask binds itself to the wearer. To remove the mask, you must either attune to it, or you (or someone else) must perform a DC 17 Strength check to pull it off. The wish and remove curse spells will also work to remove the mask.

Attunement

If you dealt the killing blow to the oni, you have earned your right to attune to the mask without complications. Otherwise, at the end of each hour that you are bound to the mask, you must make a DC 15 Charisma saving throw. You are attuned after three successes. After each failure, you suffer the following effects in respective order:

You suffer the effects of hideous laughter for 1 minute. You hear dissonant whispers and take 6d6 psychic damage. The mask tightens around your face, and you cannot breathe until the mask is forcibly removed. Follow the rules for suffocation in the Player's Handbook (pg. 183) to determine how long you can survive before the mask is removed. If you do survive, you can no longer try to wear the mask without it trying to suffocate you again. Others may try to attune to the mask with the same rules.