Zarhym (link)

Holiday bosses (such as Ahune for the Fire Festival) will now be accessible through the Dungeon Finder.

• Players must use the Dungeon Finder or speak to special holiday NPCs in the world to queue up and access these bosses.
• Upon accepting a queue for any holiday boss, the party will be ported directly to the necessary area for confronting that boss.
• The previous summoning criteria for these bosses have been removed. Players can queue up for and fight each World Event boss as many times as they want for any standard loot that they may drop.
• All rare holiday items (such as The Horseman’s Reins) will have a chance of being found in holiday-themed loot troves which will drop once for each player in the party no more than once per day, in the same manner that doing the Random Dungeon daily quest will provide a specific reward the first time it is completed in a day.