Blue is an unusually large crystalisk encountered in the Caustic Caverns. It is referenced by the ECHO recording found at the entrance to the caverns that Dahl security officer Elyse Booth had found the young crystalisk, and befriended it. When Overseer Harchek ordered that crystals be harvested from the crystalisks, the results proved fatal to the previously docile beasts and those remaining, with Blue among them, retaliated in kind. Harchek's final recording indicates that it was Blue that killed her personally.
Blue exhibits many of the same behavioral patterns as its smaller counterparts. Its ranged attacks include shooting several fast-moving volleys of spikes or a single large projectile in an arch towards the target. While the first is simple to evade and does little damage, the second will explode a short time after its contact with the ground, causing a large amount of explosion damage in a fairly wide radius. Blue's melee attacks are also similar to other crystalisks, which include stomping the ground with its forward-facing foot and causing AOE (area of effect) damage, or striking the ground with the center of its body, also causing AOE damage and knocking nearby enemies backward. In-game observation shows that Blue tends to favor its melee attacks, and so will often choose to close with a target and/or knock them into the corrosive liquid surrounding the arena in which the fight takes place.
Blue's leg crystals will regenerate a minute or two after being destroyed, restoring about 30% of Blue's health. Blue's long ranged attacks will spawn mini-crystalisks that do melee damage and which can self-destruct in a small but damaging radius. In addition, regular crystalisks will spawn during the fight.
- Main article: Safe and Sound
- Characters standing underneath Blue when he is killed will be trapped under his hulking mass as it comes crashing down. Once Blue falls and buries into the ground however, they will be able to move out of his body.
- Killing Blue before any of his leg crystals grow back completes the 'Harchek's Revenge' challenge worth a badass rank of 10.
- Blue can drop the legendary Fabled Tortoise shield upon death.
- As of Patch 1.2.0, Blue has increased health.
- Strangely, Blue can be trapped in Maya's Phaselock. This makes him one of the biggest enemies, if not the biggest, that can be trapped with Phaselock.
- A player seeking to complete weapon Challenges involving critical hits may find an ideal target in Blue and its regenerating leg crystals.