If you fight 255 battles the Cursed Shield, it will turn into the Paladin Shield(it will tell you in the message bar at the top of the screen after battle). The Paladin Shield will give you great defense and either absorb or block all elemental attacks, plus it teaches you Ultima x1. Hope this helps.
actually, you NEED ribbon equipped even to just uncurse it, too....
does anyone know the point of uncursing the Cursed Ring? (can be stolen from something in Kefka's tower or won at colleseum by betting Cursed Shield).