The Assembly of Iron went down some days ago and here's the video of it. The fight reminds a little of the bug trio in AQ40, where the difficulty depends on the kill order.

The hardmode achievement:
Heroic: I Choose You, Steelbreaker

More information about the fight:
WoWWiki

PoVs: Banai (Prot Warrior), Azisa (Shadow Priest) and Ceren (Holy Paladin).

Music:
- Red - Fight Inside
- Brand New - Handcuffs (outro)

For more 25-man hard mode movies, visit:
http://www.lrguild.org