Assembly of Iron

Overview
The Assembly of Iron is a 3-boss fight against Steelbreaker, Runemaster Molgeim, and Stormcaller Brundir. The bosses engage at the same time, so for 25-man at least 3 tanks will be required. For 10-man in the beginning of the fight the OT tanks the two smaller bosses. When any of the bosses dies, it heals the still living ones to full health, gives them 25% bonus damage, and grants them additional abilities, all through the buff Supercharge.

Steelbreaker, an Iron Giant, is a very hard hitter, and has a raid-wide AoE. His tank and the healers assigned to the tank will need to watch for Fusion Punches, which might kill the tank in seconds. Molgeim will also cast Runes of Power, which look like big blue circles on the ground, underneath Steelbreaker - they increase his damage, therefore the tank must move him out of them, and allow the DPS to enter (similarly to Malygos' sparks). After the first Supercharge (1 boss down), Steelbreaker will gain an AoE that increases Nature damage taken, so all raid members will need to watch for it. The second Supercharge (2 bosses down, Steelbreaker is the last one alive), Steelbreaker will debuff his tank with a debuff that causes the tank to die after 25 seconds, so the raid will need to finish the boss before that.

Runemaster Molgeim, an Iron Vrukyl, is a caster-type boss. He will cast Runes of Power underneath random targets, increasing the damage of anyone standing in them - everybody in the raid should try to stand in those, and make sure no bosses occupy them; Molgeim's Runic Barriers will damage any attackers, so DPS should watch their health, and stop attacking if it gets low. After the first Supercharge, Molgeim will gain a Shadow Fissure-like Rune of Death, that does damage to players standing in it. The second Supercharge will allow him to summon Lightning Elementals, which will run to a random player and explode, inflicting damage to players in 30 yards range.

Stormcaller Brundir, an Iron Dwarf, requires more than just tank and healer paying attention. His spells are more AoE oriented, and the raid will need to watch for both Overload, which he uses since the beginning, and Lightning Whirl, which he gains after the first Supercharge. Brundir will also use Chain Lightning, which increases the Nature damage taken by the affected targets. While there is at least one more boss alive, Brundir will be both tauntable and stunnable - this doesn't hold true if he is the last one alive. If Brundir is affected by two Supercharges, he will start to chase random raid members, inflicting huge amounts of damage every second to anyone near them.

Tactics (10-man version)

Kill order:
Steelbreaker - Runemaster Molgeim - Stormcaller Brundir

Phase 1:
MT1 on Steelbreaker. Tank him in the south of the room.
MT2 on Runemaster Molgheim and Stormcaller Brundir. Tank them in the northeast of the room, and focus on interrupting the chain lightning. (needs his own healer in the northwest of the room , keeping distance to avoid overload and chain lightnings)

MT1 has to move Steelbreaker out of the Rune of Power everytime it is cast on him. The healer( on him need to be able to remove magic everytime Fusion Punch is cast by Steelbreaker (only priests and paladins can do this). You need to move him so that he is barely out of the rune, while all DPS (all melee, ranged when available) can still stand on the rune to receive the 50% damage buff. Use Bloodlust/Heroism as soon as you can get a nice DPS spree on him with all melee standing on the rune just after moving him. Save the Bloodlust/Heroism for phase 2 or 3 if you aren't sure.

MT2 has to tank both runemaster and stormcaller during this phase. Preferrably a mage will assist him to spellsteal the runemaster's shield while DPSing Steelbreaker, otherwise you need the healer on MT2 to dispel the shield (only priests or shamans can do this).

Phase 2:
As soon as Steelbreaker dies, MT2 should use his cooldowns to reduce damage, while MT1 picks up the Runemaster and pulls him to where Steelbreaker was tanked before (the south of the room).
From now on, the Stormcaller will additionally spam Lightning Whirl so you should have your mage ready to interrupt whenever MT2 can't do so. Mind that you can use most kinds of CC to stop him from casting, stuns (etc.) work just as good as interrupts.
The Runemaster will use Rune of Death from now on on random raid members, so you need to keep running from it.
Just keep interrupting the stormcaller and dps the runemaster until he's dead.

Phase 3:
Once the Runemaster is dead, the Stormcaller will keep spamming Lightning Whirl and additionally use Lightning Tendrils from time to time. Basically, as soon as he uses the Lightning Tendrils ability, everyone should clear the area around him.
Players targeted by this need to run away until he either targets someone else, or lands. During this phase ranged DPS can still maintain DoTs on him, but still should prefer to keep distance to him and should save any DPS until he lands again.
Probably most important thing is this phase is that all your melee DPS is 100% alert to when he casts Overload. They have to run away the very moment he starts casting it, otherwise they will most likely die and you'll lack the DPS/interrupts to finish him off.