Lord Marrowgar

Health:
25 Man: 23,700,000
25 Man Heroic: 31,376,000
10 Man: 6,972,500
10 Man Heroic: 10,500,000
10 Minute Berserk
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Abilities:
-Saber Lash - Inflicts 200% weapon damage (300% in 25 man) split evenly between the target and its 2 nearest allies. [Let your tanks do the pull, make sure they're the first ones there. And the rest of the raid, don't be anywhere near them.]
-Coldflame - Inflicts 6,000 Frost damage every 1 second to everyone standing in it. [The raid itself can avoid most if not all the Coldflames if they stand inside his gigantic hitbox. Hunters are out of luck though. The fires appear to spawn just outside his hitbox and shoots outward, so the inside is never hit.]
-Bone Spike Graveyard - Impales 1 random players (3 in 25 man) in a Bone Spike, which does 9000 physical damage and then 10% of their maximum health every second until destroyed. Bone Spikes have 39,000 health on 10 man and 63,000 health on 25 man. [The dps should be switching to these and breaking them out asap. If the raid is grouped up together, stacking, it would help minimize any run time melee has to make.]
-Bone Storm - Attacks nearby enemies in a whirlwind of bone. Does more damage the closer you are to him, about 6000 damage every 2 seconds on top of him, 800 damage when far away. [Raid spreads out and avoid blue flames. Also, aggro is reset after this is finished, so dps hold back just a little until tanks reach him. Repeat the above stuff until Bone Storm occurs again.

https://www.youtube.com/watch?v=zFTceGrZIVk
http://www.downfallguild.org/Lord-Marrowgar
If you have any question, feel free to ask them below.
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Hardest boss in ICC, no bullshit, it really is.

Indeed

Indeed my ass!