Less-rabi made even easier:

1. Get 3 ICC geared DPS
2. Interrupt him once

Done

Seriously it's really easy now with the current gear, you can easily kill him before he casts transformation a second time. And even if you're a little slower then that, the second cast is easily interruptable as well.

I believe counterspell doesn't work as his transformation is a physical ability, not a spell.

Basically you have to either
1) kill him within 5 seconds after the first cast is interrupted
or
2) kill him within 5 seconds of the second cast being interrupted while the boss is above 35% which requires some pacing.

Trying to interrupt the 3rd cast with any amount of latency? good luck with that.

@Thyrial

I've run it with 3 ICC geared DPS and we always hit the 3rd transform and then he transforms again a spit second later and screws us out of the achievement. We're probably getting screwed by server lag, actually.

Are you talking about people in full ICC25 gear that pull over 10K dps each?

I've seen a strategy that suggests that you take your time down to 50%, saving your nukes and cooldowns, then unload after the second or third transform. However, it's never worked for me.

@Eyhk

Counterspell dose work, the game counts it as a spell and you get the full 8 sec lockout. I've gotten my own and many guildies Les-Rabi using it.

@Krick

Moorabi has 431,392 hp. In order to kill him before the second cast, you have 10 seconds till first cast, 3.8 second cast, and then 5 seconds before the next cast for a maximum of 18.8 seconds. That boils down to a overall party dps of 23,000 dps or 4.6k dps per person if all 5 people are dpsing. If you have three 10k dps people in the group there is absolutely no reason why you should hit two transformations let alone three.

The trick is to interrupt as late as possible. The first cast is 3.8 seconds so even interrupting at the 3 second mark gives you a good 8 seconds to kill him. Also have the tank and healer dps as well, since nobody at that gear level should be dying from Moorabi in 18 seconds.

@Kaz

Never tried it with a mage so I couldn't say for sure but if it does work, 3 seconds more is nice for lower dps groups. So from 50% you have 3.8 second cast time + 8 seconds spell lock to kill him, which should be more than enough time. Interrupting at 3 seconds will give you 11 seconds to burn 50%, basically ends up to 3.9k dps per person, which any heroic geared person should be able to do, especially with heroism/bloodlust.