How to Earn the Less-rabi Achievement in World of Warcraft: Wrath of the Lich King

In order to earn the "Glory of the Hero" Achievement and your Red Proto-Drake, you will need to get some very tough Heroic Dungeon Achievements, one of them being the infamous "Less-Rabi". To pull this off, you need to run Gundrak and kill the last boss, Moorabi, without letting him turn into a mammoth. This is one of the hardest Heroic Achievements you will ever attempt.
Step 1Bring the right group. As with all Heroics, you will need a healer, a tank and three DPSers (DPS stands for Damage Per Second.) For this Achievement, an extremely high DPS group is needed. Earning this Achievement hinges on two things: spell interrupts and killing Moorabi in a horribly short time span. Your DPSers will need to be geared with Naxxramas gear or anything higher.

Step 2Bring Interrupts. In order to prevent Moorabi from turning into a Mammoth, you need to hit him with a spell interrupt at the right time. Many classes have spell interrupts. Shamans, Death Knights, Mages, Paladins (post-patch 3.1) and several others. You will need at least two, preferably three interrupts. Timing is critical in order to hit Moorabi's casts.

Step 3Get the right mods. You will need a mod/addon that displays cast times, so that you can see when Moorabi is casting his "Transformation" spell (which turns him into a mammoth.) XPerl is one of the most widely-used mods and makes it easy for you to set up cast timers with. You will also need some kind of stopwatch. Whether it's in your hands or in an addon (preferable) is up to you. It is absolutely critical that you have a timer; Moorabi's Transformation is automatically cast at certain points in the fight. You will need a stopwatch to tell you when these times are, so you can be ready for them.

Step 4Learn the timing. Moorabi will always cast Transformation at 10 seconds into the fight, 20 seconds into the fight, when he hits 50% health, and then every five seconds after he hits the 50% mark. To summarize:

Transformation Cast
10 seconds
20 seconds
50% health
50% +5 seconds
Every 5 seconds thereafter

Have your interrupt ready at the appropriate time so you can prevent him from transforming. Note that the more times he is able to cast Transformation, the shorter his cast time gets. If you cannot kill Moorabi by his fifth Transformation, you will probably fail.

Step 5Save your cooldowns. While timing is critical, knowing when to break out your big guns is also critical. Save your cooldowns for when Moorabi hits 50%, then blast him with everything you've got. Pop trinkets, Avenging Wrath, Heroism, whatever you've got. Once he hits 50%, you have very little time to burn him down before he begins casting Transformation very quickly.

Step 6Practice. Nobody gets this Achievement the first time through. It requires pinpoint interrupt timing, massive damage and a ton of quick-burst damage to burn him down before he can transform. If he transforms, just run out of the instance (up the stairs to the left of where you fight him) and try again. Your tank will probably need to stay and keep him busy while the party exits and the encounter resets. Constant death can wear heavily on a tank's gear, so think about chipping in for your tank's repair bill.