Ring of affliction

A ring of affliction was a cursed magic item that appeared to be a ring of resistance.

Powers
The ring actually functioned just like a ring of resistance until the caster attempted to use the ring's magic to resist an opposing school of magic that it was attuned to, at which point the wearer would find it more difficult to resist the effects of whatever triggered the magic. Once activated in this manner, the curse of the ring prevented it from providing the benefits of a ring of resistance and could only be removed from the finger by a remove curse spell.

Notable Owners
Nhar-del, a Zhentarim wizard inhabiting the Dalelands, wore a ring of affliction attuned to necromancy.