Note: This quest chain was removed from the game with patch 3.0 (WotLK expansion), since Onyxia no longer requires any attunement. These instructions can still be used in WoW Classic Era/vanilla (level 1-60) as Horde to get the Drakefire Amulet and enter Onyxia’s lair.
- Go to Kargath in Badlands in Eastern Kingdom and speak to Warlord Goretooth in the tower. Keep asking him questions until you get the item
Warlord Goretooth’s Command. Right click the item to start the quest “Warlord’s Command“. - Go to Lower Blackrock Spire (LBRS) and kill Overlord Wyrmthalak, Highlord Omokk, and War Master Voone. Also retrieve the Important Blackrock Documents that randomly spawn on the ground beside either Wyrmthalak, Omokk or Voone.
- Return to Warlord Goretooth in Badlands to complete the quest.
- Get the next quest from Warlord Goretooth called “Eitrigg’s Wisdom“. You need to find Eitrigg in Orgrimmar. He’s in Grommash Hold, the big building in The Valley of Wisdom. He will not be marked on the mini map, so just look around at the NPCs. Speak to him and he will send you to Thrall, who is just a few yards away in the same building.
- Get the next quest from Thrall called “For The Horde!“. Go to Upper Blackrock Spire (UBRS) and kill Warchief Rend Blackhand. You may need a raid of 10 for this. Get his head and return it to Thrall for a nice trinket.
- Get the quest “What The Wind Carries” from Thrall. All you have to do is ask him some questions. Complete the quest.
- Get the next quest called “The Champion Of The Horde” from Thrall. You have to speak to Rexxar who “wanders the desert wasteland of Desolace, travelling between Stonetalon and Feralas.” Here are maps.
- He gives you the next part called “The Testament of Rexxar“. Go to Sorrow Hill in Western Plaguelands and find Myranda the Hag.
- She gives you the quest “Occulus Illusions“. Go to UBRS and kill dragons and collect their eyes. It’s easy with a raid and you’ll collect them quickly. Return to Myranda the Hag when you have 20 eyes.
- The next part called “Emberstrife” is easily soloable even though it’s an elite quest. Just go to Dustwallow Marsh and find the southernmost cave. Wear (and use) the amulet Myranda gave you to turn into a dragonling and be able to talk to Emberstrife. He will give you three quests, so it’s a good idea to have enough free slots in your quest log. You have to kill three dragons and you can do them in any order.
- For “The Test of Skulls, Scryer“, go to a cave in Winterspring and find and kill Scryer. A party of 3-5 will easily take him down. Be sure to loot his The Skull of Scryer.
- For “The Test of Skulls, Somnus” find Somnus in Swamp of Sorrows. He is on patrol, so he moves around. 3-5 level 60s will take him down quite easily. Make sure to loot The Skull of Somnus.
- For “The Test of Skulls, Chronalis“, Find Chronalis in Tanaris, at the Caverns of Time. Be sure to loot The Skull of Chronalis.
- Return the quests to Emberstrife and get the next quest in the chain: “The Test of Skulls, Axtroz“. Travel to Wetlands and find and kill Axtroz. He is slightly harder than the others, but 4-5 people can kill him without breaking a sweat. Be sure to loot The Skull of Axtroz and then return it to Emberstrife to complete the quest.
- In the next part, called “Ascension…“, you seek the advice of Rexxar again. So go back to Desolace and travel the road between Stonetalon and Feralas to find him. He will send you on a quest called “Blood of the Black Dragon Champion“.
- Go back to UBRS and kill General Drakkisath. Be sure to loot Blood of the Black Dragon Champion from his corpse. Then return to Rexxar and turn in the blood. He will give you the Drakefire Amulet that you need to get into Onyxia’s Lair. Congratulations!
As for Onyxia’s Lair, it’s located in Dustwallow Marsh at 53.77. You need to wear the Drakefire Amulet or have it in your backpack, be in a raid and be at least level 50 to enter.
Onyxia’s Lair is at 53.77 in Dustwallow Marsh in Kalimdor. You can use an addon like Leatrix Maps to display coordinates.