Cataclysm is officially underway, and with new zones, new quests, new dungeons, and a plethora of other new things, it's not hard to get lost in the shuffle of what is actually happening with the lore. Case in point, while questing in Hyjal, you'll meet a familiar gnome who has a problem. It's related to Hyjal, but he sends you all the way over to the other side of the world. In a mole machine no less. Blackrock Caverns is one of the new 5-person dungeons for levels 80-81. Let's take a look inside.
The gnome who you meet in Hyjal is none other than Finkle Einhorn. If you've ever been to Upper Blackrock Spire and fought The Beast, killed him, and skinned him, you'll remember finding Finkle inside. Thanks to his trusty lava suit, he survived the belly of the Beast and now he's assisting the Guardians of Hyjal in investigating Ragnaros' return to Azeroth. Apparently Finkle's an expert on the matter due to his previous exploits. Of course, we could have told him we saw Ragnaros and Deathwing having a little heart to heart as we flew into the zone for the first time. Regardless, Finkle informs you that the Twilight's Hammer Cultists are moving elementals between Hyjal and Blackrock Caverns. Along with Finkle's bodyguard, Raz Skullcrusher, you hop in the mole machine and show up on the doorstep of the instance.
Blackrock Caverns is physically located near the entrance to Blackrock Spire. Upon entering, you'll start the quest chain with Finkle and Raz that involves you chasing a crazed Orc throughout the instance. Rather than regurgitate the quest line to you, let's take a look at the bosses of the dungeon and see what exactly they're up to, and how it relates to what is going on in Hyjal.
Bonecrusher is the first boss of the instance. He's an Ogre Lord working for the Twilight's Hammer Cult under the leadership of Cho'gall. When you reach him, he's torturing and interrogating Raz, presumably to find out what he's doing in the Blackrock Caverns. Once defeated, Raz is released, but he's not quite the same Raz.
Next you'll come upon Corla draining the energy from a Nether Drake into other cultists. She is a high ranking member of the Twilight's Hammer Cult, using her abilities to take that drained energy and turn regular cult members into drakonids. She's not afraid to die, for death is what all of the cultists are devoted to. But to save Raz and to prevent the cultists from becoming drakonids, die she must.
Like all good armies, the cult is in need of armor and weapons. Karsh Steelbender is the resident evil blacksmith making the necessary equipment. He also happens to be in your way as you chase after Raz.
Beauty is most likely the mate of The Beast from Blackrock Spire. She also happens to have a litter of puppies named Lucky, Spot, and Buster after the dogs of 101 Dalmations. No matter how cute you think they are, Finkle doesn't think leaving her or her litter alive is good for anyone, so you'll have to take care of Beauty just like you took care of The Beast.
Lord Obsidius is the last boss of Blackrock Caverns, and introduces us to a new class of enemy, the Elemental Ascendant. These elementals appear to have originally been Twilight Cultists who through a ritual or draining of power from other elementals, have ascended to a new form. Obsidius appears to be the one in charge of all of the operations within Blackrock caverns, orchestrating the transport of elementals, armor, equipment, and the transformation of cultists into drakonids. Obsidius claims he cannot die, so it's possible we will see him later on, perhaps in the Twilight Highlands. or at least he will not be the last Elemental Ascendant we see.
Taking it all in at once, Blackrock caverns appears to be a staging ground for the Twilight's Hammer Cultists to supply troops, equipment, and magically created monsters to the battle for Hyjal to fight against the druids there. Thankfully, with Finkle and Raz's help, you're able to cause quite a lot of damage to their operations, and hopefully swing the battle in the Guardians of Hyjal's favor.