- Order: Leviathan
- Suborder: Sea Wyvern
- Infraorder: Thunder Shell Wyvern
- Family: Lagiacrus
The Lagiacrus is one of the most famous and feared Leviathan, a group that also includes Agnaktor, Uroktor, Royal Ludroth, Gobul , Nibelsnarf, and Kuarusepusu. Lagiacrus also has two different variants, Ivory Lagiacrus, Lagiacrus that have been feeding on quartz, and Abyssal Lagiacrus, old individuals found deep in the abyss.
In the New World Lagiacrus are found in the Deserted Island and Flooded Forest. Despite its ability to come up on land, they prefer to stay by deep waters. They rarely need to travel far from water, due to the abundance of prey in both of their tropical environments. Lagiacrus have been seen within the Primal Forest, Misty Peaks, Ruined Ridge, Jungle, and even in waterways in other parts of the Old World.
Lagiacrus is the top predator of its habitat, and even predators such as Rathalos and Rathian prefer to keep out of its way. Of course being the Lagiacrus' only real competition besides each other, the Fire Wyverns would be considered a threat to a Lagiacrus, as would a Lagiacrus to a Fire Wyvern. Lagiacrus's control of Thunder Element makes it a dangerous adversary in the aquatic habitat it resides, even for the well defended Gobul of Flooded Forest. Even Plesioth that migrate to the Deserted Island and Flooded Forest would be wary of the large and powerful leviathan as its powerful electrical attacks can easily cripple or even kill the Piscine Wyvern. This would cause Plesioth to avoid Lagiacrus and its two Subspecies at all costs. Lagiacrus are known to feed on fish, lobsters, Kelbi, Aptonoth, and Epioth.
The only known predator of the Lagiacrus is the Elder Dragon Nakarkos, which has been observed using its electrical organ to perform electric attacks of its own.
Lagiacrus is a large, blue aquatic leviathan, adapted to life in tropical waters. Its hood-like structure is allows it to swim through the water much quicker along with the help of its tail and limbs. Lagiacrus are able to stay submerge underwater for up to half a day without coming out for air. The large dorsal spikes on its back are used to release its electric attacks alongside a possible electro sac below each spike. Its able to release this electricity by contracting its cells at high speeds inside its muscles. When it does this some of the electricity actually combines with some of the mucus in its mouth, allowing it to spit out lightning projectiles from its mouth. In other regions, the Lagiacrus is able to bend the lightning it creates around it, how it does this is still unknown.
Lagiacrus are highly aggressive Leviathans that is the "Lord of the Sea". To hunt down and capture prey, Lagiacrus will swim in a circle to form a whirlpool. These whirlpools are used to suck up fish and other prey so Lagiacrus can shock them to death before feeding on their quarry. These whirlpools are occasionally used sink boats and ships.