Encyclopedia Magica: Acorn of Wo Mai

 

Acorn of Wo Mai

Wondrous Item, Artifact (requires attunement by a creature of good alignment)

Aura: Overwhelming Abjuration

The Acorn of Wo Mai is  a large lead acorn-shaped vessel almost three feet in height and encircled by golden bands inscribed with arcane characters. Though it appears to be tremendously heavy, it can be carried with relative ease. It sometimes makes a faint thumping noise and is warm to the touch.

According to legend, the Acorn of Wo Mai is the prison of a powerful fiend, summoned by powerful war-wizards before escaping from their control. Though the fiend could not be killed, it was eventually defeated and bound in irons thats it could not break and imprisoned inside the vessel that would be known as the Acorn of Wo Mai. Sometime since, the Acorn was lost.

The fiend within has hearing and normal vision out to a range of 60 feet and can communicate telepathically with any creature that attunes to it that understands at least 1 language. It tries to hide its true nature and stresses the need for secrecy. The fiend is generally friendly and helpful and actively provides good advice. The fiend eventually requests that the party help to free it once it believes it has convinced them of its good intentions.

Spells. While attuned to the Acorn, you can use an action to cast the Polymorph spell. Once you have used this ability three times, you cannot do so again until the next dawn.

Random Properties. The Acorn of Wo Mai has the following random properties:

-Two minor  beneficial properties

-Two major beneficial properties

Destroying the Acorn.  The inscribed characters on the golden bands must be damaged by a +3 or stronger weapon to weaken the seal, and the vessel cast into the heart of a volcano, whereupon the fiend is released. The exact nature of the fiend is up to DM discretion, though a Balor, Pit Fiend, or something of similar (or greater) Challenge Rating would be appropriate.

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Well, the first artifact I've come across while converting the Encyclopedia Magica to 5e. for an artifact, it is much less of a powerhouse than other artifacts presented in the DMG, leaning much more strongly on the plot device angle. Still, as far as plot devices go "the seemingly benevolent entity that turns out to be super evil once set free" is a classic.