Observed (10 player)

What an awesome title-- it's perfect for a Balance Druid. :D

Kill Algalon the Observer on hard mode. Since Algalon has no normal mode, engaging him is enough to activate hard mode. To engage him, you will first have to do several other encounters on their hard mode:

Complete the Iron Council encounter on medium mode (Runemaster Molgeim last) or hard mode (Steelbreaker last)to allow 1 player to loot an Archivum Data Disc. This allows that player to obtain the sigils from Hodir, Thorim, Freya and Mimiron by killing them on their hard modes. These 4 sigils are required for the Algalon quest. Completing the Algalon quest rewards the Celestial Planetarium Key. Once Yogg-Saron has been killed, this key can be used to unlock the Planetarium where Algalon resides.

There are some who question the existance of Algalon's hard mode. Let this developer quote take away your doubts:

Hard mode is hard. Some hard modes are harder than others. Then there's Algalon the Raid Destroyer. He feeds off of your tears.

It is possible that your are not allowed to loose any raid members to Algalon during the raid lockout, since this is also true for the Heroic counterpart.

Because no one has tested either Yogg-Saron or Algalon, he will be the hardest boss in Ulduar simply because you need to have done hard modes on other bosses to even access him. Treat him as an optional extra boss and not an optional boss.