WoW Retail, Unlimited Respawn Mobs In Legacy Raid (Patreon)

EDIT: Although this always worked on only some toons, I think it has now been completely fixed, though its very difficult to say for certain. I'll continue checking this every patch cycle.

The talented Youtuber Golden Routes sent me the following slightly cryptic message:

I have a video idea for you . Pretty sure it's an exploit :P. Onxia's Lair for Rugged leather and hides.

 One the mobs shouldn't drop those skins, it should be borean leather, two the mobs are on a timer respawn if the boss isn't killed while it's in it's flight form

What Golden Routes is referring to is this: In Onxyia's lair in Dustwallow Marsh there are a number of "Onyxian Warden" mobs guarding the tunnel that leads to the raid boss herself.  

If Onyxia is taken down to 50% of her health, she begins flying and casting fireballs-she will do this until you attack her again. The warden mobs respawn in the tunnel during this phase. Moreover when killed they respawn continuously-every 15 seconds. The mobs drop standard Wrath Of The Lich King loot - you may wonder why it is wotlk loot-the reason is that the original Onyxia's lair was changed during Wrath patch 3.2.2 to its current incarnation.

The mobs can also be skinned for rugged leather (you will need 150 skinning skill in classic skinning in order to profit most from this). 

The most simple way to take advantage of this farm is to use an aoe ability and loot-this is very easy to automate even without special software. 

This is a very interesting farm with what seems like a lot of potential for further development. I noticed that beginning the Onyxia fight also caused the wardens to spawn-so potentially hunters may be able to use feign death/play dead to make the farm even faster. 

TLDR

1. Enter Onyxia's Lair. Kill warden mobs.

2. Aggro Onyxia.

3. Take Onyxia down to 50% health.

4. Return to tunnel, kill all mobs that attack and loot/skin Onyxian Wardens.

Be careful not to kill Onyxia accidentally when reducing her health-once she dies you are locked out of the raid until reset. I used a caster and this is easily accomplished by using melee attacks. Melee classes should unequip their weapon and maybe other gear if necessary to prevent an accidental kill.

When farming the wardens it is best to use an ability such as talented flamestrike which ticks continuously after cast, if you have one-this allows you to kill the mobs the instant they spawn.