"A great deal is made of the most powerful demons, those that create abominations and those that have changed the history of Thedas. It is often forgotten that not all demons are such awe-inspiring beings. Some that break through the cracks in the Veil into our world are known as wisps, a sliver of a thought that once was. A wisp 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--often, so we've found, by other demons. What remains of its mind clings tightly to the one concept that created it--a hatred of all things living.
While its ability to target a living creature is limited, these wisps often mindlessly attack when encountered in the Fade. In the living world, they often have been known to maliciously lure the living into dangerous areas, being mistaken for lanterns or other civilized light sources. This does, however, seem to be the very limit of their cunning."
--From the journal of former Senior Enchanter Maleus, once of the Circle of Rivain, declared apostate in 9:20 Dragon Age.