Hello,
This exploit is for farming the Defias hand and leg pieces. I personally was interested in farming these for my own transmog without having to pay 5k per piece on the ah. There isn't a huge demand for these pieces so I doubt you can make much money farming them just to sell them.
I guess I'm not the first person to find this bug but I tried to search for it and didn't find it.
Quick version:
1. Sap one of the Defias Overseers
2. Kill the other overseer
3. Re-stealth
4. An additional overseer will respawn after a second
5. Repeat 1-4. It doesn't matter which overseer you kill, just dont kill them both. Vanish if you aggro the only remaining overseer somehow.
Long version:
The defias overseer mobs in the Deadmines (normal lvl 15 version) are the only mobs who continue to drop Defias leather set pieces.
The mob I am referring to is the neutral (non-hostile) defias overseer, between the 2nd and 3rd bosses in the deadmines.
Sadly they only drop the gloves and legs. Usually you can only kill 2 of these mobs (with a 2% drop chance per mob that they will give you either of the pieces) per dungeon clear. I discovered that if you sap one mob, kill the other, and then reactivate stealth, that the mob which you sapped will reset and another overseer mob will spawn. This means you can kill an overseer mob every 5 seconds rather than killing 2 mobs every few minutes (usually you have to clear up to the mobs and then run out and reset the dungeon).
This seems to be because the overseer mobs have a script where they have a 2-way conversation, and the one mob left alive after you restealth requires a second mob to interact with. I discovered this by accident when I was leveling a new character and attacked these mobs, killed one but the other bugged out and evaded until it reset, causing a third overseer to spawn.
This isn't hugely useful, although I have sold the pieces I farmed on the ah for about 1k each which has been a great help for me as it was my first character on that server. In the first farming session I had 2 gloves after 30 minutes. In the second I had 4 leg pieces after 10 minutes. It does vary so if you attempt this, be patient. A bot can probably farm dozens of pieces in a few hours.
If you do this as a rogue, taking glyph of stealth and the first tier talent to reduce focus cost by 75% in stealth will allow you to sap, ambush and re-stealth non-stop and kill 1 overseer every 5 seconds. Just be careful not to kill both of the mobs as you will have to run out and reset the dungeon. If you aggro both mobs (or the only remaining mob) by accident you can vanish to reset them.
This probably works for other classes with combat resets, but a rogue can sap one mob, kill the other and restealth within 5 seconds indefinitely and I don't think any other class can replicate this.
I did this on my lvl 40ish rogue and as a result I did not 1-shot the second mob if I accidentally hit it. As a lvl 100 you will definitely 1-shot the second mob if you hit it by mistake, so watch out.
This is obviously an exploit as you can kill one overseer every 5 seconds rather than only killing 2 for each dungeon clearance which takes several minutes. Its only really useful for obtaining the pieces if you want to farm them yourself. I didn't feel like it was worth the time to farm them and sell them but I could be wrong. There might be other mobs in the game which can be exploited similarly, though I couldn't think of any off the top of my head and the defias overseer is distinct in that it is the only mob which drops the mentioned items.
Edit: one thing I forgot to add, the mob which is left alive after you restealth will give the message 'target is in combat' if you try to sap them for several seconds after you have re-stealthed. It is quicker to target the new mob which has respawned and sap them, and then kill the 'older' mob.