Heroic: Majordomo Fandral Staghelm

You will have the Concentration Bar, that will increase your damage and healing done by the percentage of concentrated you are ( 100 point grants 100%, 50 50%, etc). The problem is, that your concentration is lost when you are hit from an attack.
Why do you need this? Well, after SHannox HC i checked his HP: it is no more than only 480 million in 25 HC ( OMG)
So yeah, gl for downing him :)

An update on rilgania's method to maximise dps for lower dps groups.
Fury, the buff that the boss gains each time he shapeshifts, which increases scythe and leap damage. Note that, it doesnt increase melee and other spell damage of boss.
The idea is to skip scrop and avoid getting damaged by leap.

For scrop, tank should blow cooldown and eat the first scythe away from the raid. Spread out to cat phase immediately after first scythe. (or just spread out 2 sec before the cooldown for the 1st scythe ends)

For cat, have melee deal with the spirits and keep range in clusters. Range should keep an eye on boss's energy, when energy reaches 100, start moving to avoid getting hit by leap.

You can repeat this indefiantely untill the boss enrages.

edit: Beth has been nerfed in a hotfix and might be easier now.

Do yourselves a favor and tackle this boss before Beth'tilac. He might even be easier than Alysrazor, I'm not sure about that. We never downed a Cata HM boss or even end boss like Ragna as fast as this one. I think. No boasting here, that's how it worked out for us. And we're nowhere near the top!
But really, he's downright easy if you get a few basic things right:

scorp:
- start with scorp phase, leave 3 DDs out (ours were MM hunter, BM hunter, rogue) in first, 1 (rogue) in the following, and 0 when he's got 6 fury stacks and more.
- in the 1st scorp phase, wait for up to 12 cleaves (or more if you handle it), stack raid CDs. in the following scorp phases, take 6 or 7 cleaves. use raid CDs everytime they're ready (should be in the 3rd scorp phase) to delay the transition.
- everyone who can should be using defensive CDs to mitigate high damage bursts at the end of the scorp phase.
cat:
- hero/lust as soon as everyone has maxed out concentration
- always do 7 stacks in cat, spread well, positioning is key to avoid healrange and concentration issues
- assign the orbs well; we used tank/melee and hpally/spriest for max damage. mind that the ranged orb soakers should keep distance between each other to prevent charge damage.
- make sure that a melee has maxed out concentration for most of the fight to cleave down the adds.

this is for 10m. i neither know nor care about 25m :P