First Glimpse at Algalon the Observer

Update 3: Added a sneak peek video of Algalon. (Thanks to Underground Kosmonavts)
Update 2: Algalon's abilities added (thanks Wraith for the input).
Update 1: Exorcism can no longer be used on players

I just received several pms from a few members of the well-known french guild Wraith, they were able to unlock the famous hard mode only boss on 10-man: Algalon the Observer.

As you can see in this screenshot, you only have one hour per week to defeat Algalon.

Valnoth, a Lead World Designer confirms this.

Algalon's Abilities

thanks Wraith for the input

	Ascend to the Heavens Inflicts 655500 to 724500 Arcane damage to enemies.
	Big Bang Inflicts 107250 to 112750 Physical damage to nearby enemies.
	Black Hole Explosion 15675 to 17325 Shadow damage inflicted to enemies.
	Cosmic Smash Calls an abyssal boulder from the sky, dealing 46250 to 53750 Fire damage.
	Phase Punch Massive blow that inflicts 8788 to 10212 damage and slowly fades the target to another plane of existence for 45 seconds.
	Quantum Strike Strikes at an enemy, inflicting 23750 to 26250 Physical damage.

Unlocking Algalon

In order to unlock this boss, you need to obtain the key of the Celestial Planetarium. The quest that enables this can be accepted at the Archivum Console, which is located in a room behind the Assemly of Iron.

Defeat the Assembly of Iron at hard mode by completing I Choose You, Runemaster Molgeim or I Choose You, Steelbreaker to loot the Archivum Data Disc.

With this questitem, you get a quest to obtain the Sigils of the 4 watchers of Ulduar, which combined open the door of the Celestial Planetarium.

Defeat the Freya at hard mode by completing Knock, Knock, Knock on Wood to loot the Freya's Sigil

Defeat the Hodir at hard mode by completing I Could Say That This Cache Was Rare to loot the Hodir's Sigil.

Defeat the Thorim at hard mode by completing Lose Your Illusion to loot the Thorim's Sigil.

Defeat the Mimiron at hard mode by completing Firefighter to loot the Mimiron's Sigil.

Finish the quest accepted earlier and for that week you have unlocked Algalon the Observer, the boss that has hard mode only and despawns after 1 hour of tries for that lockout period.