I’m more acquainted with the 10 man version so this is what I’ll be focusing on, with some additions for the 25 man version.
Without further addue, I bring to you
Simple enough fight and you should kick his arse long before the enrage timer starts flashing red. He has three abilities that concern you, the small and slightly undergeared (if you’re reading this you’re just stepping into ICC and don’t have the gear yet) shaman. The first one is called Bone Cemetery. What he does is to target a random player (non tank) and impale him with a Bone Spike. You will be unable to move cast, drink a pot, Thunderstorm and whatnot. You will also take a moderate amount of damage over time that will need to be healed through until you escape. To get out of it you will need your raid to dps the spike until it’s dead. There’s an achievement to doing this too. All Spiked players must be released within 8 seconds of impale and you get BONED. Get it?
The second ability (or first, in order of cast) is Coldflame. This will start at the bottom of his hitbox and head towards a wall in a straight line. In the classical style of Don’t stand in bad shit, you should run away from it as soon as possible, preferably before it reaches you. It will do a damage per tick kind of thingy and a lag spike might kill you. Healers will need to be on the ball with damage from coldflame because it usually happens that once a bone spike is down you will find yourself in the coldflame. For the most part, this is avoidable damage and you shouldn’t be taking it at all unless spiked.
- To avoid this ability you can stand behind the boss, inside his hit box. The flames will start just outside it and you’ll get no damage and will be close enough for melee to DPS the spike, if you’re chosen.
- If you go ahead and do this make sure that you’re not ahead of the tank on the pull. You won’t grab aggro but he does a cleave like melee swing that is shared between the tanks. Learned this the hard way.
The last of his abilities is Bone Storm. He will drop aggro and whirl around the room chasing random players. Big ass radius for the damage on this one but totally manageable with a couple of good healers or just one. If you want to play it safe you can run towards the closest wall (thus putting some distance between his melee whirlwind swing towards his current target and you). This is a very good time to refresh your water shield if you’re having mana problems, because you will get hit and you will get some mana back. You can also use TS at this point, it’ll do the damage and give you the mana. I would suggest however keeping it until the spike he does is close enough for TS to do some damage on it. Instant cast decent damage? Good!
- If you have good healers you can actually ignore the running jumping part of this, the damage is in the 4k-ish area per swing if you’re using a shield and you can keep DPSing Marrowgar merrily.
After a Bone Storm is finished it’s all rinse and repeat.
Time your Bloodlust/Heroism for after a Bone Storm for maximum DPS uptime. A god time to use it is after the Storm that he does when Marrowgar’s in the 2 mil-ish HP area.
Most of the bosses in ICC do a truckload of physical damage and unless your tank/s is a druid who asks you for Strength of Earth Totem, go with Stoneskin as your Earth Totem.
Fire Totem. Oh, the possibilities! If you have a Demonology Warlock that is specced right you can and should not use ToW. Instead use Fire Elemental Totem and Searing Totem when the first one expires. Watch its timer and refresh when needed.
Water Totem. If you have more than one paladin in the raid chances are you have GboW and the safe choice is Healing Stream Totem. It’s not much but it helps and your healers definitely won’t mind it.
Air Totem. Depending on the composition of your raid, you can:
a) Use Wrath of Air if you have at least another caster DPS in the group. Your healers will be thankful for it as well. This is the default choice.
b) Use Windfury Totem if you have good healers but not so awesome melee dps and no Frost Deathknight DPS.
The only difference with the 25 man version of Marrowgar is that he will spike 3 people at once and will have more HP.