Hey there.
My guide today is about this achievement:
The Undying - Achievement - World of Warcraft
This achievement is one of the "harder" ones. And you can make profit of this.
Look for 9 other people who are willing to earn some money. Usually you will have guild mates which already did that achievement for this.
Now go grab a Naxx ID and kill everything but Kel'Thuzad. You have to play as you would do the achievement so nobody may die during a boss fight.
If you manage to kill all bosses up to and including Sapphiron you made it.
Go to Dalaran and put a message in trade chat:
"WTS Naxx ID cleared up to KT and nobody died during any boss encouter so you can easily kill KT for "The Undying" achievement".
The trick is the achievement is only saved on the instance id which makes selling possible. You can also invite single players to your group which pay you money. Everything is possible here.
So this would be something like:
"WTS spot in group for Undying achievement (guaranteed kill)".
You have to add something like "if you don't mess with the shadow fissures" or anything like that. The rest should be fine.
It's up to you how to use this. You can even bring your friends. Have fun
Btw yes, you can do the same thing with the 25-man version of this achievement but I doubt that there are many people who actually manage to do this like it was nothing
Edit says: Didn't know where to put it as it's a guide and an exploit in one thread. The achievement says defeat every boss, so this is NOT intended.
Edit2: Some people added prices, 10.000g for Undying and 25.000 for Immortal so that's roughly an extra 1000g for everyone in the raid.
Confirmed by Blizzard:
Blizzard has officially confirmed that this is working.
Here is a link to the blue post:
World of Warcraft - English (NA) Forums -> The Immortal
This is for both, Undying and Immortal.
They didn't state if it's intended though so I think they will be working on a fix for it.