Frozen Berserker

 
Prerequisite(s): Ability to Rage.
 
Benefit: As long as you are under the effects of a barbarian rage, you gain the cold subtype. You gain immunity to cold, but have vulnerability to fire, which means you take half again as much (+50%) damage as normal from fi re, regardless of whether a saving throw is allowed, or if the save is a success or failure.
 
Source: Frostburn