Credit to our friend Klog for finding this little gem : http://media.mmo-champion.com/images...r/magmawww.jpg
I know it looks funny, but it is a serious and simple tactical explaination!
A bit more depth about his abilities and what to do: http://www.wowwiki.com/Magmaw
As you can see, raid composition will be very important, we could have major problems and exponential parasite spawning with too many melee - ranged AoE are going to be the real stars in this fight.
He is also protected by trash:
"Just before the Magmaw pull, there will be two hostile enemies guarding him that are pulled at once. They are capable of a strong, nature-damage Thunderclap, which will two-shot non-tanks if they are allowed to stand together. They will often Charge the player that is farthest away from them, dropping all current aggro and generating 300,000 new threat on the Charged target. In addition, when one dies, the other will Enrage.
Have the two tanks pull each enemy to opposite sides of the room, and have the healers and ranged stand in the center. The tanks should have their backs to the walls, while the melee should have their backs to the ranged. This nullifies any issues from Charge. After that, just make sure that the HP of the adds is watched fairly carefully, and try to kill them at the same time. " - WoWWiki.
+ Essentially, we have a stay out the fire fight in some respects, but with major duties on all three roles - tanks will have to be on their ready, healers will have not only the duty of healing the tanks as they take huge damage - but also will need to remember to swap over their earth shields/beacons etc.
+ Some important points from that article that need emphasizing:
1. The cooldowns - Magmaws ability cooldowns begin after the cast, not after completion of the ability or the "spike" phase.
2. The melee DPS are going to need to co-ordinate chains - this is a great time to speak up on vent rather than listening to my blather
3. Tanks - you can still target his vulnerable spot whilst mangled - Your DPS will become hugely important at this point!
For the first few tries, we're going to worry about tactics - avoiding the fire, killing/kiting parasites, and getting chains co-ordinated. DPS won't matter, neither will getting him down. Focus on watching the screen, not your ability bars.
TACTICS: ARGALOTH (BARADIN HOLD)
If we do end up going to BH, you'll need to know this: http://www.wowwiki.com/Argaloth
But it can be explained in a nutshell - it is a tank-swap fight, tanks taunting after every meteor slash, groups should stack on their tanks, run out to avoid the firestorm, then collapse back. Its actually as simple as that. The only other thing is that dispellers are going to be on their watch.