The Tenth Boss
Strategy
Before entering combat, your raid should equip all the fire resistance they have. Tanks should have 305 resist, melee classes should have 200 resist, and the rest of the raid should have a resistance of 150.
The Ragnaros boss fight can be split into two phases: one where the boss can be attacked for 3 minutes, and the other where the elemental lord submerges and summons eight fire elementals that linger for 90 seconds, or until they're killed.
The boss uses several main abilities: Melt Weapon, which randomly reduces melee weapon durability by one each stack, Elemental Fire, which deals 4,800 damage to the tank over 8 seconds, Wrath of Ragnaros, Which activates every 25 seconds, knocking back all melee classes or killing them instantly. It is vital that the melee DPS disengage to avoid this spell.
At certain points during the encounter, Ragnaros will use Hand of Ragnaros, dealing fire damage to a random caster as well as all nearby allies, knocking them back and stunning them for 2 seconds. To avoid this attack as much as possible, your casters should thin out whenever Ragnaros is present. Finally, whenever no one is within close range of the boss, he will use Magma Blast which will whittle away your raid. Be sure to keep your tanks alive and on the boss whenever he appears.
Whenever the boss disappears, he will summon eight Sons of Flames which can be Banished by Warlocks during the fight. In addition, each elemental uses a passive ability called Lava Shield which will drain the mana of nearby players. After 90 seconds, or whenever all the elementals are dead, the boss will reappear and everyone should return to their original positions from phase 1 to re-engage the boss.