Garr (world boss)

Garr is a rare elite boss-level lava elemental found to the west of Sulfuron Spire on Mount Hyjal.

Strategy
Garr has six Firesworn following him. These can be pulled separately from the boss and should be killed before Garr is pulled to make him considerably easier. Everytime a FIresworn dies, they will deal roughly 50,000 damage to anyone close to them so melee should move away when they're about to die.

Once all the Firesworn are dead, the tank can pull Garr. Ranged should try to stay at maximum range. Garr will periodically dispel any magic buffs the group have and will cast Magma shackles on the group. This should be dispelled from melee as soon as possible.

Every 30 seconds, Garr will begin to cast Massive Eruption. All melee must run away from Garr when he begins casting this or they will die. If you do die, it is possible to release spirit and rejoin the fight.

Other than the slow debuff and the Massive Eruption, this is a rather straight-forward fight.