Age of Conan's upcoming world boss system. The most recent game director's letter explains that these bosses are an outgrowth of the anniversary event designed to make the game world feel more dynamic. Each boss will have a one-week spawn period, and with 12 bosses in total, players will be facing a different boss each month.
The boss will spawn within one or two outdoor areas and can be engaged and fought by any level-appropriate characters within those areas, with rewards going to anyone who takes part in the fight and survives for at least one minute before it dies. Item caches are dropped by each individual boss, but the bigger reward comes to players who manage to be counted as slaying all 12 bosses as they spawn. For more details, as well as information about upcoming gathering and event changes, take a look at the full game director's letter.