Nocturn

Nocturn is a villain and one of the antagonists in the Bionicle series. He was an amphibious being who was imprisoned in the Pit for his crime of destroying his own home island in a blind rage. He was also one of the few creatures who was partly immune to the mutagen in Mahri Nui. He later became Ehlek's lieutenant when the latter found him in the Pillars of Salt.

Past
Nocturn was originally a resident among his amphibious fellow beings in his home island until one day when he loses control of himself, he eventually succumbed to his murderous rage and destoyed his island with a single blow, thus resulting its destruction. Soon after being defeated by both Axonn and Brutaka of the Order of Mata Nui, they summoned Botar to banish him to the Pit to be imprisoned for his crimes.

Quest in Mahri Nui
After the Great Cataclysm wrecked the entire Pit, Nocturn and the others, including the Barraki were freed from their imprisonment and eventually made their way into the ocean of Mahri Nui. However unlike the Barraki, Nocturn was completely immune to the mutagen of the ocean due to his amphibious traits. Soon afterwards, Nocturn took refuge in the Razor Whale's Tooth where he spent most of his life there.

After quite sometimes, when a sea squid spotted Nocturn in his hiding place, it went back and reported to Kalmah, who reported to the other Barraki. Pridak then sent both Carapar and Mantax accompanied by a few Zyglak  to fetch him and to be brought him before him.