Aumthurax's Ring of Shapes

This mizzium ring was crafted by the mages of Morgrave University as partial payment for the magical forging services of the red dragon Aumthurax, The Forgemaiden.  The ring is crafted of mizzium and has fine details making it look like a fox chasing its own tail.   The ring makes the wearer immune to shape changing magic and abilities like polymorph, unless the wearer chooses to allow the magic to take effect.  The ring can store a total of 9 charges and restores 1d6 charges per day.  The ring lets the wearer cast Alter Self for 1 charge, Polymorph for 4 charges, and Shapechange for 9 charges.  (If the dragon casts polymorph on an unwilling creature, the DC is 19.)

Notes: Wear the ring for a day then focus at least 50 hp of magical fire damage on the ring while you wear it.