Noxxion

Noxxion is a living symbol of the corruption of Maraudon, created by Lord Vyletongue.

Dungeon Journal
''Noxxion is a living embodiment of corruption. Theradras ordered her ally Lord Vyletongue to create this putrid elemental to be a powerful servant and a loyal pet to ease the princess's loneliness. Noxxion spreads its toxic essence into areas of Maraudon that have not yet withered under Theradras's malign influence.''

Group strategy
Because all damage is nature, plate armor does not help. You may want to consider using the character with the most hit points as your tank, which may be a feral druid. When Noxxion's Spawns appear, you can opt to have a paladin with Consecration go in. It is difficult to hold on to aggro, and this is where groups will most often fail on this boss. Use AoE to handle the spawns, heal up if possible (bandages), and then concentrate on Noxxion when he re-appears again.

Quest

 * Servants of Theradras