The Dark Iron Pact (Horde)

If you're like me and are trying to do this quest without much knowledge about Blackrock Depths, here is a quick guide:

1) Enter Blackrock Depths through Blackrock Mountain (fly down towards the lava pit where the Molten Core NPC is standing, then enter the doorway and follow the tunnel)

2) Once inside, open your map and walk straight to where Lord Incendius is

3) Kill him and progress until you reach the square room with golems. Here you can kill Fineous Darkvire

4) Once at the circular area, go to the right corner(there'll be a bunch of mobs there) and use any leap/jump over there (Hunter disengage, DH glide, Warrior Leap etc)

5) Go into the first doorway on the right side and you will see the NPC that offers the quest

6) Progress naturally through the dungeon killing Ambassador Flamelash and after that entering the room of the Trial of the Seven, killing them, completing the quest :-)

Bonus 7) You will be able to grab another quest afterwards. In the large room, kill a "Shadowforge Flame Keeper" on the north and south end of the room and pick up their torch (/tar Flame can help). Use the torch at the top and bottom fire pits in the back of the room. This opens up the door to the final two bosses and allows you to finish that quest aswell.

Hope this helps someone!