Algalon the Observer is a hard mode-only encounter in Ulduar, released in patch 3.1. Algalon was sent by the titans after Watcher Loken's death activated a planetary fail-safe protection, indicating possible distress on Azeroth. Algalon's task is to analyze any systemic corruption on the planet. If it's deemed beyond saving, the Titans will "re-originate" the planet to cleanse it of corruption, killing all currently living organisms in the process.
He can only be accessed if least one member of a raid has obtained the Celestial Planetarium Key or Heroic Celestial Planetarium Key in Heroic mode. Players have a one-hour window to defeat him per lockout period, starting upon first initiation of the encounter. Blizzard has sardonically referred to him as "Algalon the Raid Destroyer".
<ref>tags exist, but no
<references/>tag was found