Kraken the Abyss Lord

Kraken the Abyss Lord, disguised as an NPC called Nerakk, was originally the quest NPC for the «Deep Sea Plunderers» quest, but was later revealed to be the boss of the quest. The Kraken has 7 HP bars.

Background
Kraken's goal is to steal the egg of a Prince from the Underwater Temple to take his revenge against the Aesir. However, the temple was protected by a magical barrier that prevented him from entering it. Thus, Kraken disguised himself as an old man by the name of Nerakk and requested help from fairies to retrieve the egg, under the guise that some robbers had stolen a pearl, which he was planning to give to a friend, from him and hid inside the temple.

Appearance and Abilities
In his human form, the Kraken looked like an old, wrinkled man with a long, octopus tentacle-like, gray beard, thick gray eyebrows and long gray hair. In his true form, the Kraken is a large octopus-like creature with bright red eyes, rectangle pupils, 6 large and 2 smaller tentacles and a large circular mouth hidden behind its front two tentacles with several layers of teeth.

The Kraken is a powerful creature that, according to Yui, has stats higher than even those of Aincrad Floor Bosses. Even with indirect hits, he was able to deplete Kirito's HP to the red zone in one strike. The Kraken is also able to regenerate damage done to his tentacles.

Attack Patterns
The Kraken has only been shown using his tentacles to attack its opponents. It may also have an attack that involves its mouth, but such an attack was never executed due to being interrupted by Leviathan.

Boss Battle
If players discover that the "pearl" is actually an egg and refuse to give it to Nerakk for deceiving them, he will transform into Kraken the Abyss Lord and fight the players. In his true form, the Kraken easily dispatched Kirito, Klein, Agil and Lisbeth in mere moments while they were unable to land a scratch on the beast due to its regenerative ability. However, at that point, Leviathan the Sea Lord interfered by throwing his trident in front of the monster, forcing the Kraken to retreat.

Trivia

 * Kraken the Abyss Lord is based on the legend of the Kraken in Norse mythology.
 * Nerakk's name is rearranged letters of Kraken, hinting to his true form.