I did a search on this and didn't see this posted so I thought I would share. If it was posted already I apologize. Also, if this is well known, I also apologize.
In Naxx when you get to the Pipe, have everyone stand on the pipe right before the tunnel. Send a high mitigation/avoidance tank, a healer, and either a Shadow Priest or Hunter down the pipe. Once at the end, you can glitch Gluth to jump up and into the pipe, eliminating the adds completely.
How to do it:
Hunter puts himself just in range to see Gluth and shoots. Pressing the side strafe keys repeatedly (by default these are Q and E if you never changed your keys) and it will glitch him in and out of combat. You will see him dance around almost mimicing your movements. It will take a couple of shots to get him fully up there, as each time he moves closer twitching. Next thing you know, he is at the top of the tunnel. Tank picks it up and drags Gluth towards the pipe and your raid party.
Basically this is 100% easy mode. Decimate isn't a factor, and Enrage is the only concern but you should easily burn him down before the timer.
I have had my guild try this a couple times and it worked both times, so it is not nerfed yet.