Plesioth are Piscine Wyverns introduced in Monster Hunter. They are known to inhabit aquatic environments and can be encountered at low, high and G-ranks.
Plesioth are bipedal monsters with a wyvern-esque body structure. They have webbed feet and a paddle-like tail, and are covered in shiny, fish-like scales. Their mouth is filled with shark-like teeth, and their eyes glow a bright yellow. Their head and back feature large fins which can fold in and out at will.
Plesioth can fire highly pressurized jets of water at foes, and can use their massive size and weight to crush and batter attackers. They are highly adept at swimming and are both agile and deadly in the water.
Plesioth are ambush predators, adapted to stalking prey from the water and attacking by surprise. They can occasionally be seen on land.
HC Plesioth has much more muscle mass and more tinted color with spotted wings. Its moves are more land based and aggressive, as it will perform sweeping water beams, body slams, sleep causing liquid, fake sleep, charges on foot with which it will try to run hunters over with its sharp spiked feet and jumps that it can even U-turn mid air to body slam then slither.
Monster Hunter Freedom 2 / Monster Hunter Freedom Unite
An enormous, flightless, aquatic wyvern with wings that have evolved into fins for swimming. Although superficially fish-like, they can move on land as well. They love frogs.
Monster Hunter 3 Ultimate
Giant piscine wyverns with swift and varied underwater movements, as well as deadly breath and charging attacks. Plesioth are agitated by loud noises, so approach warily. Their favorite food are frogs.
Monster Hunter Frontier G
It can be fished out with a Frog in certain areas, when being fished out, the Plesioth will not enter rage mode, as well as move for a few seconds giving hunters plenty of time to deal great damage.
Using a Sonic Bomb is an easy alternative to fishing out a Plesioth. Just be cautious that it will enter rage mode upon recovering.
The dorsal fin can be broken by hitting the Plesioth in the belly.
When near death, Plesioth won't enter rage mode if affected by a Sonic Bomb's sound.
When near death, Plesioth will put its dorsal fin down.
If Plesioth is killed in water, it will sink and then come back up and float on the surface. This, of course, means no carves are possible. This is not an issue in Monster Hunter 3 Ultimate.
Plesioth's design is based off of an unknown species of shark.
Beware of the Plesioth's shoulder/hip attack, as it can hit and damage you even when you are on the other side of the direction of the attack.
Plesioth can limp, but this is very rare.
Plesioth returns, where the hunter is able to fight it underwater as well as on land.
Plesioth will lower its back fin when hungry. After it regains stamina or becomes enraged, it will raise its back fin again. When close to death, it will actually limp instead of lowering its back fin.
Plesioth will sleep in area 11 of the Deserted Island in order to recover health, unlike Leviathans, which flee to area 12.
Additionally, with the introduction of underwater combat, Plesioth can now be killed underwater and still be carved.
The fin on Plesioth's head (as well as the head itself being scratched), and on its wings can now be broken in addition to its main dorsal fin.
Plesioth can recover its stamina by eating Epioth in Area 10.
It can also eat from the Epioth corpse in Area 11, although this is less common.
Interestingly enough, Plesioth is interested in land-based prey as well, as it is seen preying on an Aptonoth in the Plesioth Ecology cinematic.
Plesioth's Hip Check hit boxes are for the most part fixed, and they no longer strike as wide an area as before. Its tail spin also has more realistic hitboxes, dropping lower to the ground as Plesioth bends its knees when spinning.
The Plesioth can be hit with a Fishing Harpoon to make it drop a shiny.
Plesioth is fought differently than in the main series. You control a Wyvern Hunting Boat to fight Plesioth at Great Fortress Lake, using a cannon to attack the monster.