One additional boss has been added to every raid from Naxxramas all the way to Icecrown Citadel with a storyline following throughout. You can start your raiding journey by speaking to Aion Solus at The Temple of Order in Storm Peaks.
New boss locations (10man):
-Naxxramas: Tyranastrasz - The Elder Consortium of Alexstrasza
-Ulduar: Vision of Madness - Servant of the Dark
-Trial of the Crusader (Argent Tournament Grounds): Decayed Devilsaur - The Wandering Beast
-Icecrown Citadel: Agitha - The Bone Maiden