Less-rabi

Me and my guildies recently got this achievement after our share of failed attempts and here is how we did it:

First off, we did NOT use Blood Lust/Heroism.

Next (and this is most important) we figured out the exact time of his casting intervals (from the beginning of one cast to the beginning of the next):

• 
  
• 100%-51% he will cast his transform every 10 seconds.
• 
  
• 50%-0% he will cast his transform every 5 seconds.
• 
  

What we had to do from here was preempt all of his casts.

To do this, start your in-game stopwatch when your tank pulls. See when he casts the first transform and from there time each in 10 or 5 second intervals depending on what percentage he is at.

I got lucky and started it right on time so his casts went at :10, :20, :30, :35, and :40. Each person with the interrupt should be watching his own timer to avoid voice-chat or Vent lag.

If you are good on the timers you should be able to interrupt each transform the split second that he begins to cast. We had the casts so well timed out that all we were seeing were interrupted cast bars. Like it has already been stated: His cast time goes down as he loses health, so if you aren't able to interrupt as he starts you may not get to see his cast bar at all anyway.

That is basically all there is to it. Just being prepared for what is coming instead of waiting until it is going to happen.

Our actual kill was what started off as "practice" on the timer strat and we very easily got the achievement.

We also had plenty of interrupts in the group. Our makeup was:
Death Knight (tank)
Enh Shaman
Arcane Mage
Ret Pally
Holy Pally

Even though we had enough people to constantly interrupt this could just as well have been done with only a couple interrupts on short CDs like Kick, Shock, or Pummel.

Best of luck!

Strangulate doesn't work, at least not on heroic. He's immune to silences, just interrupts work. So Mind Freeze yes, Strangulate no.

Ok, after trying and failing at many of the possible strats below I found a foolproof Super easy way of doing this achievement. Group can have any make up save 1 spot for an elemental shaman with 5 of 5 reverberation. his cooldown of earthshock will then be 5 seconds which is exactly moorabis time between casts on transformation after an interupt. I was the elemental shaman and did nothing but interrupts (I ended up interrupting 4 times because removing a dps slowed the fight) I did all the interrupts. All I did was spam my earthshock button for the entire fight starting with the first inter