Rare Encounter

From DDO wiki

Within a wilderness adventure area, there are fixed locations where rare encounters have a chance to spawn. These are usually mini-bosses that replace a normal spawn of monster, but might require talking to a non-hostile npc. Killing the mini-boss or completing the goal the npc has completes a quest, which grants reduced experience on further completions. Completing all of the Rare encounters in a area will grant a larger experience award.