Styx Dragon

The dragon can breathe air and water.

Creatures afflicted with this disease are incapable of regaining hit points in any way until the disease is cured. Additionally, as their flesh starts to rot, a creature with this disease takes 36 (8d8) Necrotic damage after each long rest they finish.

The dragon is immune to all negative effects from the River Styx.

The dragon can use its Frightful Presence. It then makes three attacks using its Bite, Tail, or a combination of the two. It can replace one of the attacks with Constrict.

Melee Weapon Attack +14 to hit, reach 5 ft., one target. 19 (2d10 + 8) Piercing damage plus 7 (2d6) Poison damage, and the target must make a DC 19 Constitution saving throw. On a failed save, the target contracts Stygian Wasting.

Melee Weapon Attack +14 to hit, reach 10 ft., one target. 15 (2d6 + 8) Bludgeoning damage. If the target is a Large or smaller creature, it has the Grappled condition (escape DC 22). The dragon can't make a Tail attack while a creature is Grappled in this way.

The dragon tightens its grip on a creature Grappled by its tail. The creature takes 27 (3d12 + 8) Bludgeoning damage, has the Restrained condition until the start of the dragon's next turn, and must make a DC 19 Constitution saving throw. On a failed save, the target contracts Stygian Wasting.

Each creature of the dragon's choice that is within 120 feet of the dragon must succeed on a DC 18 Wisdom saving throw or have the Frightened condition for 1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the dragon's Frightful Presence for the next 24 hours.

The dragon exhales poisonous Styx water in a 60-foot-long, 10-foot-wide line. Each creature in that line must make a DC 19 Dexterity saving throw, taking 54 (12d8) Poison damage on a failed save, or half as much on a successful one. Creatures that fail the save contract Stygian Wasting.

The dragon makes a Wisdom (Perception) check.

The dragon makes a Tail attack. If a creature is already Grappled, the dragon may use Constrict instead.

If the dragon has successfully Restrained a creature with the Constrict ability, it may throw them up to 100 feet away. When it lands, the creature takes 21 (6d6) Bludgeoning damage and must make a DC 18 Constitution saving throw. On a failed save, the creature has the Unconscious condition for 10 minutes.