Actions

Multiattack: The Leviathan Wyvern can make two Bite attacks on its turn. It cannot make two attacks if one is not a Bite.   Bite: Melee Weapon Attack. Reach 20 ft. single Target, +8 to hit. On Hit: 17 (2d10 +6) Piercing Damage and 12(3d6) Lightning damage. If the target is a Creature of Medium size or smaller, the Leviathan Wyvern can choose to Restrain it in its mouth. Targets Restrained this way take 1d8 Piercing damage at the start of each turn they are pinned. A restrained target makes a DC 18 Strength saving throw at the start of each of its turns while held in the Leviathan Wyvern's mouth. The Leviathan Wyvern cannot Bite another creature while holding one in its mouth, but has advantage on creatures restrained this way.   Slam: Melee Weapon Attack. Reach 15 ft. +8 to hit. The Leviathan Wyvern chooses one side of its body and launches its torso sideways, bodychecking any targets it comes into contact with. all creatures it impacts take 15 (2D8 +6) Bludgeoning Damage and, if the Leviathan Wyvern's Pulsing Cuirass is active, 12(3d6) Lightning Damage. All creatures hit by a Slam attack must make a DC 21 Strength saving throw or be thrown 10 feet back and knocked Prone.   Tail: Melee Weapon Attack. Reach 20 feet. +8 to Hit. The Leviathan Wyvern sweeps its tail in a wide arc around itself toward a target. All creatures between the target and the tail, including the target, with an AC below the Attack roll take 1D10 +6 Bludgeoning damage and are pushed backward 10 feet. If this attack doesn't break the AC of a creature before the target in line, the attack instead ends at this creature without doing damage to it or anything after it in the attack's damage order.   Lightning Mortar: Ranged Weapon attack. Range 90 ft. Single target, +7 to hit. On hit: 21(2D12+8) Lightning damage. The Leviathan Wyvern launches a blob of hypercharged mucus at a target it can see within 90 feet, dealing a considerable amount of Lightning damage on a hit. Targets that are hit must make a DC15 Constitution saving throw or be Stunned for a round.   Discharge: The Leviathan Wyvern releases all its pent-up elecrtical energy in a massive burst, ionizing the atmosphere surrounding it in a brilliant display of lightning and thunder. Any and all creatures within 15 feet of this living Tesla coil must make a DC 20 Dexterity saving throw, taking 23(3d10) Lightning damage on a failure, and half as much on a success. The Leviathan Wyvern can only Discharge if it has at least three (3) charge counters on it. Upon using this attack, the Leviathan Wyvern's Pulsing Cuirass automatically activates and lasts for its full duration.

Bonus Actions

Charge: The Leviathan Wyvern begins charging up its potent electricity for a massive attack or a defensive layer, adding a single Charge Counter to itself.

Legendary Actions

The Leviathan Wyvern has three (3) Legendary Action Counters with which it can engage an enemy. it can only use one Legendary Action at a time, and only once per turn at the end of another creature's turn. Some Legendary Actions require more than one Counter, so be attentive to the Cost Requirement listed next to each Legendary Action.   Bite (one action): The Leviathan Wyvern makes a bite attack against a target within range.   Tail (one action): The Leviathan Wyvern makes a tail attack against a target within range.   Lightning Mortar: (two actions): The Leviathan Wyvern makes a ranged Lightning Mortar attack against a target it can see within range.   Amped Tackle (three actions): The Leviathan Wyvern Launches itself forward with driving force, releasing any stored electricity while it surges forth. It moves forward 120 feet in a straight line. Any and all targets in the way of the Leviathan Wyvern must make a DC 22 Dexterity saving throw, taking 20 (2D10+8) Bludgeoning Damage and 16(3D8)Lightning Damage on a failure, and half as much on a success. creatures who fail the Dexterity save are also knocked Prone as the Leviathan Wyvern continues over them until it reaches the end of its tackle. any Charge Counters the Leviathan Wyvern has saved up are removed during this attack, forcing it to start collecting charge again.

Suggested Environments

Any coastline with signifcant sunbathing space and a proper ecosystem upon which to feast will draw a Leviathan wyvern to come lay claim to territory. These behemoth predators are not deterred by colder water conditions or distance, as some have been found as far inland as moutain lake systems. All they require is a sufficiently large body of water, a sustainably large prey population, and a place to beach themselves for a nap.