- Order: Leviathan
- Suborder: Sea Wyvern
- Infraorder: Thunder Shell Wyvern
- Family: Lagiacrus
Abyssal Lagiacrus is a part of the Leviathan class. This Leviathan is rarely seen due to its habit of hunting for prey in the dark depths of the ocean. Its existence has been known for many years but remained impossible to prove as it was only in ancient text. The Abyssal Lagiacrus's true identity is a powerful, 100-year-old Lagiacrus, or Ivory Lagiacrus, individual that has gotten bigger over many years and has completely moved to the dark sea due to its immense size.
Abyssal Lagiacrus are known to live in the darkest part of the sea. The only real possible place to hunt one down is in the Underwater Ruin if one happens to travel in it.
Abyssal Lagiacrus was once the top predator in the shores of its previous environment but now it isn't able to easily catch some larger prey due to its new lifestyle. Abyssal Lagiacrus now specializes in catching deep-sea prey like fish and some species of lobsters. Rarely, Abyssal Lagaicrus can catch prey like Epioth. The only known monsters that could potentially be a threat to this monster is an adult Gobul, Ceadeus, Goldbeard Ceadeus, Nakarkos, and Ancient Serpent.
An average Abyssal Lagiacrus is approximately 3969.3cm long. The Abyssal Lagiacrus lives in the deep depths of the sea. From living in the dark depths, Abyssal Lagiacrus's scales have become darker in color to help it camouflage. Though it has become darker in color, some of its scales have an eerie glow to them. This is due to Abyssal Lagiacrus constantly being charged up with electricity, unlike younger individuals. Abyssal Lagiacrus is constantly charged up due to a different organ from its Shell Shockers, known as an Dynamo. Very little is known about this organ, though it is being researched by the Hunter's Guild. It is said that this organ turns the sea around it into an electrified weapon. In order to catch prey, it uses its glowing scales as a tool to attract deep-sea prey to its location. This makes catching prey easier for it. Just like its younger kin, Abyssal Lagiacrus use whirlpools to capture and drown prey.
Abyssal Lagaicrus are dangerous predators that can be compared to Elder Dragons in strength. Though very little is known about its life, Abyssal Lagiacrus are feared to be the gatekeepers of the underworld.