Patch 5.3 introduces four new Scenarios and Heroic modes for six Scenarios including two previously released encounters. Whether you’re Horde or Alliance, you’ll be able to get in on the action with the use of the Dungeon Finder or by queuing (in the case of Heroics) with two of your friends.
New Scenarios

Blood in the Snow
There is a clear and present danger to the dwarven capital that Varian Wrynn isn’t going to let slide due to dwarven infighting. It’s ultimately Moira and the Dark Irons—along with the aid of some Alliance heroes—who step up to the plate to defend their new home, teaching the Wildhammer and Bronzebeard clans a lesson in loyalty and the value of fighting together for a common cause. You’ll be asked to step forth to aid Moira in this story-driven Scenario.
This Scenario is a part of the Battlefield Barrens storyline.
Dark Heart of Pandaria
Something’s afoot in the Vale of Eternal Blossoms. Garrosh has sent Goblin engineers to excavate a mysterious artifact. However, their efforts seem to have stirred up more than the crew can handle on their own. Your mission (should you choose to accept it) is to go into the Vale and do a little much needed clean-up. Things aren’t quite right in the Vale and it seems Garrosh is looking for more leverage in the battle with the Alliance.
This Scenario is a part of the Battlefield Barrens storyline.
Secrets of Ragefire
Concerned with the recent disappearance of his scouts, Vol’jin has recruited the Bilgewater Cartel’s elite Gob Squad unit to investigate. Having tracked the culprit to an abandoned section of Ragefire, you’ll assist the Gob Squad in their search and help put a stop to whoever is behind these abductions. Doing what Goblins do best, you can bet there will be plenty of explosive action. You know it’s serious business when they even call a pool pony into play!
Battle on the High Seas
The war between the Horde and Alliance isn’t confined to land. You’ll need to take to the High Seas in this Scenario and fend off enemy forces to prove your faction’s naval might isn’t to be trifled with. Once you’ve made sure the ship is safe, you’ll need to swing into action (watch out for rope burns) and make sure the enemy doesn’t have a chance to send another boarding party or take another shot. There’s more at stake than pride.
New Heroic Mode

A Heroic difficulty option has been added for Scenarios, allowing those who have the right stuff to ramp up the challenge. This mode is available for the four new Scenarios—Blood in the Snow, Dark Heart of Pandaria, Secrets of Ragefire, and Battle on the High Seas—and two previously released Scenarios—Crypt of Forgotten Kings and A Brewing Storm. To queue for this new mode, you’ll need an item level of 480 (ilvl 480) and some well-seasoned (but not too salty) friends to join you.
Taking on Heroic Scenarios will award Valor Points and a chance to obtain Raid Finder-quality items. You’ll also be able to complete a bonus objective for additional Valor. It’s important to note that you’ll only be able to earn bonus Valor within Normal or Heroic, but not within both on the same day. Random Heroic Scenarios will reward a Heroic Cache of Treasure and 120 Valor Points for successful completion of the instance.



Source : Patch 5.3 Scenario Preview - World of Warcraft



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