Hex dragons have learned to channel their pain and anger into terrible retributive magic; many foes who succeed in wounding a hex dragon find themselves wishing they could take back the blow. On any round in which a hex dragon is injured (taking Hit Point or ability damage), the dragon may curse one of the opponents who injured it as a free action.
A successful Will save negates the effect. A hex dragon may bestow a curse from younger age categories, if it so chooses. The Save DC against this curse is 10+ (dragon's HD ÷2) + dragon's CHA modifier.
Should a hex dragon ever be killed or mortally wounded (reduced to negative Hit Points), it reflexively unleashes a death curse against all creatures within a radius equal to 10 feet per age category. All creatures within the area must make a Will save or suffer the effects of this Retributive Curse. The Save DC against this curse is 10+ (dragon's HD ÷2) + dragon's CHA modifier.
The effects of this curse increase as the dragon ages:-
Based on the entry in Dragons Magazine '343 May 2006