Ruins of Adventure
Ring of Medusa's Bane
This item appears to be a simple, unadorned steel ring.
When a command word is spoken, the ring grows and changes, taking the form of a buckler shield of solid steel construction and mirror-bright finish. The shield appears immediately, properly strapped in place. A second command word causes it to resume ring form.
The shield functions as a normal buckler, granting no additional bonus to Armor Class, but does grant the wielder a +4 bonus on saving throws against Petrification attacks. In addition, the shield functions as a mirror with regard to creatures whose gaze-based attacks can be turned against them.