Mazthoril is a huge and deep icy cavern - populated by the Cobalt Brood. Within these caverns lies the true stronghold of the blue dragons, the forces of General Colbatann. Guarding this stronghold is an entire legion of dragonspawn sworn to protect Mazthoril. Night elf forces - including those rare few wintersaber riders who can tame the feral frostsaber cats - often clash with the dragonspawn legion, using blade and fang in an attempt to rid themselves of the malevolent dragons.
The blue dragons here are primarily on watch for activity from the black dragonflight, although there have recently been concerns that the blue dragonflight will be needed to assist the dragons at Mount Hyjal if the demons in Darkwhisper Gorge attack. Since Deathwing's disappearance after the battle of Grim Batol, the black dragonflight's members have been busy fighting each other for dominance. To this end, the blue dragonflight organizes an army here, lead by the dragonspawn General Colbatann, to protect the world from the increasing threat of the black dragons. Specifically, Colbatann focuses on the protection of dragon eggs, which are being stolen by the blacks for some evil purpose.
Their matriarch is the radiant Haleh - only encountered in high elf form at the peak of the cavern, accessible by a portal rune in the cavern floor. It was she who completed the key to Onyxia's Lair for Alliance heroes (although the attunement requirement for Onyxia's Lair has since been removed). Haleh has four powerful drakes who guard Mazthoril, and leads a sizable army of highly sorcerous spawn and young whelps. Spellmaw is the brood's main patrol, and wanders a slow path around a good third of the lower section of Winterspring. Manaclaw and Scryer guard the runes at the rear of the cavern. Azurous patrols nearby regions in Winterspring for threats against the forces of Malygos. General Colbatann, a notable general of the blue flight, has also been spotted near Mazthoril.
This section concerns content exclusive to Cataclysm.
The Cobalt Brood has been removed from Mazthoril. It appears to be in the control of Umbranse the Spiritspeaker. Altered Beasts now roam the exterior of the cave, while creatures reminiscent of Outland guard the Arcane Tesseracts dotting the interior.