Patch 3.3.3 is that one will be able queue up using the dungeon finder in order to fight world event bosses such as the Crown Chemical Trio or the Headless Horseman. However, the actual extent of the changes is a bit more involved, as Zarhym clarified in a recent forums post. Here's the rundown:
- First, you absolutely must use the dungeon finder to queue for the world boss. If you just go into a random dungeon or go into the dungeon directly the boss will not be there.
- Secondly, the boss will no longer have a chance to drop the incredibly rare vanity items such as the Big Love Rocket or the Horseman's Reins. Instead, those will drop out of a special holiday themed loot trove that each person will receive the first time they kill the holiday boss on a given day, much in the same way one receives 2 frost emblems for the first random heroic they get.
- Finally, Since there's no summoning the boss, you can't bring in alts to get multiple summon chances, but you can re-queue to kill it as many times as you want. However, you'll only get the extra holiday loot bag once. Note that you'll still get the more "common" drops such as trinkets and rings and the like every single time.