Onyxia's Lair is a raid whose entrance is located in Dustwallow Marsh in the World of Warcraft game. The minimum level for this dungeon is 80. The instance was released in the Wrath of the Lich King expansion. The raid contains 1 bosses. The end boss of Onyxia's Lair is Onyxia.
Oynxia's Lair is one boss raid that was re-energised for Wrath of the Lich King expansion. Onyxia is the daughter of Deathwing, the antagonist in World of Warcraft - Cataclysm. Although Onyxia is brought back for Blackwing Descent raid, her location is not the lair as it was before. Although it is no longer the highest level raid, there are still achievements to be had and also there is a mount that drops.
The Location of Onyxia's Lair is in Dustwallow Marsh on the southern end of Kalimdor. The entrance to the raid is a giant dragons jaw the outer jaw doesn't close but there is a small jaw which needs opening for you to enter the raid. The quickest way to get to the raid is to teleport to Theramore Isle (If Alliance) then fly Mudsprocket and the either fly or travel over land to the entrance. The location of the entrance to the Onyxia raid is the north side of the large rock to the east of Mudsprocket, to the south of Wyrmbog. There is a small amount of trash that you need to kill but it shouldn't be too hard.
If you are Horde, the quickest way is to get a teleport to the Caverns of Time or to Thunder Bluff, the Tauren capital and then fly to the instance. There are no direct ports to the dungeon location. Whilst you are in the zone, you might like to try and get the non-combat pet - Spawn of Onyxia.
Onyxia is asleep when you first enter but when you get close, she will wake up and attack. The battle is in three phases. The first phase is a simple tank and spank fight, the tank needs to keep Onyxia at the back of the room. At about a third down, she will walk to the front of the room and take off. Small dragonkins will come into the office which the tank needs to pick and the dps need to kill down. Ranged need to target the boss. If timing has gone well, the adds will have been killed before Onyxia comes back down. The tank needs to take the boss to the bank of the room and keep her there. The dps need to take down the adds and the boss, when the boss dies, the adds disappear.