Horde Onyxia Quest

The horde onyxia quest starts in kargath at Warlord Goretooth on top of the tower. He will not have an ! over his head, instead you talk to him and at the end of the conversation he will give you a letter than will start the quest. You need at least friendly faction with Orgrimmar to get the envelope.

Warlord's Command
This quest requires you to goto Lower Blackrock Spire and kill Highlord Omokk, War Master Voone, and Overlord Wyrmthalak. Also you need to recover the Important Blackrock Documents. The documents can spawn on the ground at the spawn areas of Omok, Voone, Urok or Wyrmthalak. When looted they then quickly respawn at one of their 4 possible spawn locations again. They may still be at the same boss location, or perhaps a new location. You cannot complete this quest in a raid so you will need to take a 5 man group to LBRS.

After turning in Warlord's Command in Kargath you will receive Eitrigg's Wisdom. This quest sends you to Orgrimmar to speak with Eitrigg in Thrall's chamber. After that turn this quest in to Thrall to receive For the Horde! (Raid). You will need to kill Warchief Rend Blackhand for the Head of Rend Blackhand. This is easiest with a raid doing Upper Blackrock Spire, but can be completed in a very skilled 5 man group.

The next quest, What the Wind Carries, just entails you listening to what Thrall has to say. After that you will get Champion of the Horde telling you to seek out Rexxar in Desolace. You can see his paths on the Allakhazam link, he roams from northern feralas near the twin collosals all the way through desolace and barely into the charred vale in stonetalon. It might take you some time to find him along his long patrol.

Once you track Rexxar down he will have you deliver The Testament of Rexxar to Myranda the Hag in Western Plaguelands. She is in Sorrow Hill standing on a tree stump. She will send you back to UBRS to collect Black Dragonspawn Eyes for the quest Oculus Illusions. The eyes are used to make an Amulet of Draconic Subversion that you will use so you can talk to Emberstrife for Emberstrife (Elite).

You can find Emberstrife in a cave in the far south of Dustwallow marsh. He is the only creature in the cave, and you will need to use your amulet to speak to him. Sometimes he isn't always up because people need to kill him to make their UBRS keys. If he isn't up just wait a few minutes and he should spawn. Emberstrife will give you 3 quests to kill various world dragons.

• The Test of Skulls, Somnus (Elite) - Somnus is found in the eastern dragonkin filled section of Swamp of Sorrows.
• The Test of Skulls, Scryer (Elite] - Scryer is found in the blue dragon cave in Winterspring. He is right near the rune that teleports you to the top.
• The Test of Skulls, Chronalis (Elite) - Chronalis is located in western tanaris at (forgot location name, maybe gates of time?) with 2 other dragons. Just sneak by the others and you can easily get him solo.

After completing these 3 quests Emberstrife will have you kill 1 final dragon.

• The Test of Skulls, Axtroz (Elite) - Axtroz is located in Southeastern Wetlands in Grim Batol. You will need to clear a few dragonkin to find him, but he isn't too deep in there.

Once you have finished your tests of skulls you will need to find a way to energize the amulet you have received. Rexxar will help you with your Ascension.... Rexxar will give you Blood of the Black Dragon Champion (Raid). This sends you to UBRS to kill General Drakkisath for his Blood of the Black Dragon Champion. This will require a skilled raid group as Drakkisath is the most difficult challenge in all of Blackrock Spire.

Once you best Drakkisath and return to Rexxar you will receive your Drakefire Amulet the key to Onyxia's Lair.