This magic iron mask lets you take on the form of an Oni, a creature from Japanese folklore also called an Ogre Mage.
Mask of the Oni
Wondrous Item, very rare (requires attunement)
Weight: 1 lb.
While you are attuned to this magic iron mask, it melds to your face when worn and can not be removed against your will.
Oni Form. As a bonus action, you take on the form of an Oni for 1 hour. Your size becomes Large. You gain +2 to Strength-based weapon attacks and make Strength checks and Strength saving throws with advantage. This ability can be used once per day and recharges at midnight.
Oni Magic. While wearing the mask in Oni Form, you can innately cast the following spells at their base level, requiring no material components:
1/day each: charm person, darkness, sleep
The Ogre Mage
A short Dungeons & Dragons adventure for Levels 5-9
The quaint fishing village of Tideswell is on edge. Every several weeks, a hideous creature has appeared each night, destroying property and terrifying villagers. A man named Esmund has collected nearly 500 gp from the local fishermen as a reward for anyone who can stop the creature.
You are recruited by Esmund, who says that the creature is an Oni, a powerful spellcasting monster that has a hidden lair in a sea cave near the village. Esmund gives you a map to the cave and his promise that you will receive gold for killing the monster.
It’s a trap. The map actually leads to the lair of a Spirit Naga with no connection to the village attacks. Esmund is a con artist, a Mage who is using a Mask of the Oni to transform himself each night. He plans to steal the gold collected from the villagers and move on to the next town to commit the same crime.
If you thwart Esmund’s plan, the villagers give you the 500 gp, Esmund’s spell book, and the Mask of the Oni.
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