A Ring of vigour could be bought from the Dungeoneering Rewards trader for 50,000 tokens, and would reduce all special attacks costs by 1/10th of the total cost of that special attack when worn. So for example, a Dragon scimitar's special attack normally used up 55% would, when the Ring of vigour was worn, use up only 50%. After the Evolution of Combat update, the ring affects Adrenaline as Special attacks have been removed.