Astonishing Swordsmen & Sorcerers of Hyperborea.
The Circlet of Fungal Power presents itself as a typical golden crown with a velvet lining colored purple with white spots. If worn, it transforms the wearer into an Amazon warrior woman with the following attributes:
Height: 6'2, Weight: 170
STR: 9, DEX: 17, CON: 11, INT: 11, WIS: 11, CHA: 18
All other characteristics, including class, remain the same. Upon removing the crown the wearer reverts to his previous appearance and attributes, but there is a cumulative 1% chance the wearer must make a Save Vs. Transformation or have one attribute (rolled on a d6) permanently altered. The accumulated chance resets with each save, but the seventh failure results in the wearer completely transforming into Amazon form (as per the Polymorph Other spell), in addition to gaining the firm conviction that they are the heir to the throne of a far-off kingdom of intelligent toadstool people.
Inspired, of course, by this. I'm not even sorry.