Unidentified Beast

Unidentified Beast is the tentative name of a monster that appears in Mass for the Dead.

Background
A monster that was discovered by agents of the Great Tomb of Nazarick while on a rescue mission for Warrior Captain Gazef Stronoff. It had used one of its appendages to capture a contaminated Gazef. Later Shalltear Bloodfallen had to directly use her power to free the Warrior Captain and slay it herself. Along the way, when its corpse was brought to Nazarick, Demiurge theorized that the specimen is perhaps a new type of creature from the Chaos Zone.

From Demiurge's analysis of the specimen, he found that the deceased monster retains a mineral-like structure. And interestingly enough, the monster shares shape and hardness to a similar material found in the Roble Holy Kingdom.

Appearance
A large pink tentacle beast that seems to be part mollusk. Its main body is similar to a bivalve with a single glowing cyclopean eye in the shell, with tentacles emerging from the maw and beneath it, piercing the ground. When dead, the color of its tentacles fade.

Abilities
The creature's tentacles has impressive regenerative abilities, each one has a different level of regeneration. It could even shrug off a direct hit from a Floor Guardian even when its main body is targeted. Furthermore, its life force cannot be measured. However, each time it regenerates, limbs or grows new ones it exhausts itself.

Several more specimens appeared albeit with powers of invisibility that were on a level that even denizens from Nazarick could not perceive.

Trivia

 * Despite coming from the same realm as the Chaos Beasts, strangely this creature was reported to have hunted down Chaos Beasts within the cave. However in Demiurge's opinion, the two creatures may have some sort of common link given that when they die they turn into stone-like substances.
 * Momonga hypothesizes that the creature when inactive returns back to its constituent material similar to a golem.
 * After the creatures rampage in E-Rantel, survivors began referring the incident as the "invisible disaster" or the "Calamity of Cracks".