Heroic: Magmaw

The add that is summoned every 35 seconds is called Blazing Bone Construct.

They actually spawn from a Meteor (Blazing Inferno) that lands on the ground. The area it is going to hit looks very similar to the ground effect used for Pillar of Flame, the ability that spawns Lava Parasites. You want to move out of the way of the Meteor before it lands, for it deals about 75k fire damage on impact, AND leaves Ignition (fire patches) on the ground in a "S" type shape, that deal about 55k per second you stand in them (they also move VERY FAST so don't stand anywhere near them). You will die before you can get out of it, barring a good damage mitigation cooldown. It is 100% avoidable.

At 20% HP the Constructs cast Armageddon, an 8 second cast that when finished, does about 125k fire damage to the raid, effectively a wipe. So why not just have a tank grab them all and never DPS them, to avoid Armageddon? They hit extremely hard - after a certain amount you just can't heal through it (if 3 are up at the same time your tank should be using cooldowns until one is dead). So when a Construct is about to go down, have all DPS hard switch to it, to kill it before the cast finishes.

Basically, you should avoid all avoidable damage to make this fight easier. You do that, you're a lot of the way there. Which means...watch your feet! Good luck!

Differences on heroic: Every 35 seconds, Nefarian summons a new add known as a Blazing Animated Skeleteon ( or Construct, don't remember exactly) that leave a lethal fire patch on the ground that deals 50k every half second if you're standing in it. The fires move as well, so they eventually need to be kited around.

The other difference occurs at 30%. When Magmaw is at 30% hp, no more blazing animated skeletons spawn. INtead, Nefarian starts to dish out a shadow ae to random members of the raid until the raid wipes or Magmaw is defeated.