Introduced as part of a recent game update, a Wisps in Dragon Age is "...a demon that has lost its power; either it has existed in our world for too long without finding a true host or it has been destroyed...".
In Heroes of Dragon Age, wisps are a new type of hero that grants enhanced bonuses beyond that provided by normal heroes when Consumed. The greater the wisp's rarity and tier, the greater the bonus. You can get a further boost by matching the wisp's faction to the hero consuming it. Wisps exist for all faction colors and in all rarities, so be sure to keep an eye on the wisp's faction!