A boss that disarms. Blue has stated the following in regards to 2.3 Blizzard wrote:
All Disarm immunity effects in the game were changed to 50% disarm duration reduction (non stacking).
The Arms talent Weapon Mastery is going to be significantly changed. Instead of providing 50/100% chance to avoid Disarm effects, it is going to reduce the duration of Disarm effects by 25/50%. The reason for this is that having full immunity with this talent really took the idea of disarming out of the game and we want it to be more viable.
So my conclusion is that they want a boss that disarms (doing to Tanking warriors what mana burn does to a Tanking Paladin). Most guilds will have Bears tank this since Disarm doesn't bother them, but those that have Tanking Paladins will have them as an option as well.