Saber Lash

Marrowgar's first trick is that he does often 300% weapon damage (200% in 10 man) to the tank, but split among 2 others nearby him. So it's similar to Mother Shahraz, you'd want 2 other tanks to stand stack with your MT to simply soak. Possible with 2 tanks, just know that there'd be spiked up damage instead of "normal" looking damage.

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

Marrowgar will spawn these doomfire like things. It's a trail of flame (frost) that you don't want to stand in. But the simple part is that it only goes out in a straight line. So fairly easy to dodge by just strafing to the side if one heads towards you.

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

Marrowgar will impale 3 random non-tank players (1 in 10 man) doing 9000 physical damage to them, then it takes 10% of their hp per sec while they're in them. The only way to free them (no bubbles, no ice blocks) is to kill the Bone Spikes. They have 63,000 hp in the 25 man, 39,000 hp in the 10 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

Marrowgar will start whirlwinding around. Think like Leotheras. Random no aggro targetting flying around the room. He chases about 4 different targets before stopping.

The entire raid will be hit, but the damage is based on proximity to him. If you're on top of him, about 6000 every 2 seconds. Further out in his hitbox, 4000 damage. Just outside even, 2000 damage. And about 800 damage if you're 30 yards out.

Also, Coldflame still occurs during this. As the raid is probably spread out, they'll fly out in more "random" directions. But it'll be 4 at a time from each of his "sides" when he stops a bit on his target of choice during the whirlwind.

Anyways, 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.

Heroic: Bone Spikes will occur during this so have to switch to dps this phase too.

Heroic Mode Summary:

More damage, more HP obviously.

Coldflame now is more of a targeted flame. Still goes in a straight line, but not set 4 points from Marrowgar. So a bit harder to dodge, during whirlwind at least, you can still stack up to avoid it otherwise.

Bone Spike Graveyards will still occur during Bone Storms. Raid has to switch to kill them asap in all both phases now.

In 10 man, the increased damage forced us to all take up assigned positions in that inner circle. Keeps everyone close together while spread out. Using 5 points, for example N, NE, E, W, NW, or something. A half circle with 2-3 people in each.

For Bone Spikes, they're mostly ranged priority, the melee won't run into dps Bone Spikes, just handle whatever's near by, worry more about them after Bone Storm. Healers keep those up in the meantime, and BoP anyone spiked and bone stormed at the same time. Priority is survival.

In 25 man, the fight is more forgiving. You have more healers, more ranged, and more people Marrowgar can target to Bone Storm / Spike. Spread out a bit more, make sure healers and ranged are covered around the room. Again clump up as minimal as possible and heal / kill spikes when convenient. Survive!