Mask of the Implacable

This ceramic, painted mask makes its wearer into a dangerous, if singularly focused, warrior. The wearer of the mask has fast healing 3 as long the mask is worn. In addition, he gains a +4 bonus on attack and damage rolls against any foe who deals the mask-wearer more than 50% of his full normal hit point total in damage.
The bonus lasts until the mask-wearer attacks someone who hasn't dealt him more than 50% of his hit point total in damage. When that happens, the bonus ends and the fast healing aspect of the mask is suppressed for 1 hour.
A mask counts as a pair of lenses for limitations on wearing multiple items of the same type.
Craft Wondrous Item, regenerate, mark of justice; Market Price: 65,000 gp; Weight: 5 lb.
Source: Races of Faerûn