Originally Posted by LoreHi, this is Lore from Tankspot and this video will be discussing the 10-man version of the updated Level 80 Onyxia encounter.
When the fight begins, the tank should turn her around and bring her to the far wall, while the rest of the raid spreads out around her. As the original dragon encounter, Onyxia has a frontal breath attack, a cleave, and a tail swipe, so everyone needs to stay at her sides to avoid being hit by any of these. The cleave and tail swipe in particular need to be avoided at all costs, as the cleave can instantly kill even plate DPS, and the tail swipe can easily knock a careless player into the whelp pits and spawn many whelps. Having a second tank ready to pick these up can make the fight go a lot smoother, especially in the later phases.
Phase 1 is very straightforward, and a simple matter of staying alive while bringing her down to 65% health, at which point Phase 2 begins. She'll walk to the other end of the room and take flight, moving out of range of melee DPS. Once she's in the air, a very large wave of whelps will spawn along with an elite Onyxian Lair Guard. It will largely be the responsibility of the tanks and melee DPS to handle these, as ranged should be continuing DPS on Onyxia as much as possible. That said, it's not a bad idea to have one or two AOE classes help burn the large whelp waves down.
The Lair Guards hit fairly hard and have a very high damage AOE that should be interrupted whenever possible. The whelps don't do too much damage by themselves but are very dangerous in large numbers. On top of that, Onyxia will be pelting the raid with fireballs from above, so there's a fair bit of healing to keep an eye out for.
All that being said, by far the most dangerous part of Phase 2 is the infamous Deep Breath. When Onyxia chooses to use this ability, she will fly corner to corner across the room, leaving a wide path of fire on the ground below her. This will make short work of any non-tanks, and isn't particularly healthy for them either, so avoiding this is top priority. Everyone will need to be mindful of where in the room Onyxia is at all times, and when the Deep Breath warning goes out, you must immediately get to the sides of her path to avoid it. For example, here you can see that Onyxia is hovering at the north point of the room. Once she begins her Deep Breath, everyone will need to get to the east or west edges of the room to avoid it.
Once ranged DPS has brought Onyxia down to 40% health, she'll land again and begin Phase 3. This is very similar to Phase 1, and the same positioning should be used. However, there's one very dangerous addition: Bellowing Roar. This is a raid-wide fear that last for three seconds, and is followed closely by an eruption of lava from the cracks in the floor, causing a fair amount of Fire damge. Worse than the Eruption, however, is the fear's tendency to cause players to wander into dangerous areas. It's very easy, especially for melee DPS, to get feared in front of her and cleaved, or behind her and knocked into the whelp pits. It's also very common for the tank to turn Onyxia toward the raid while feared just in time for a breath attack. Anything that can be used to break or resist this fear is very helpful, such as Tremor Totems, Fear Wards, and any racial or class abilities like Will of the Forsaken or Berserker Rage.
Aside from simply breaking the fear, there's a couple tricks you can use to reduce the chances of something going wrong as much as possible. Never be within 3 seconds running distance of the whelp pits -- it's far too easy to wander in there and spawn a bunch of extras. Likewise, try to stay as far away from the front of her as possible. Given the choice, it's usually better to risk getting feared into her tail and knocked into the whelp pits than it is to risk getting feared into a cleave and dying. Ranged can almost completely avoid either possibility, but it's a bit trickier for melee. Fortunately, her hitbox is fairly large, so you can still hit her from a good distance away.
Some whelps will inevitably spawn on even the cleanest of kills, so your second tank should be keeping an eye out for them and rounding them up so that the DPS can handle it. Aside from that, it's simply a matter of keeping your positioning safe and bringing the dragon down.
Thanks for watching this video. As always, for more information on this or any other encounter, check the Project Marmot forums at Tankspot.com. If you're watching this on youtube, just follow the link in the movie details. Good luck!