Bone Greatwyrm

Multiattack. The Greatwyrm can use its Frightful Presence. It then makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +14 to hit, reach 15 ft., one target. Hit: 19 (2d10 + 8) piercing damage plus 9 (2d8) necrotic damage. Target must succeed on a DC 18 Constitution saving throw or become incapacitated. If the target is a Huge or smaller creature and this damage reduces it to 0 hit points or it is incapacitated, the greatwyrm swallows it. A swallowed creature ends up in the ribcage of the greatwyrm.

Claw. Melee Weapon Attack: +14 to hit, reach 10 ft., one target. Hit: 15 (2d6 + 8) slashing damage.

Tail. Melee Weapon Attack: +14 to hit, reach 20 ft., one target. Hit: 17 (2d8 + 8) bludgeoning damage.

Frightful Presence. Each creature of the Greatwyrm's choice that is within 120 feet of the dragon and aware of it must succeed on a DC 16 Wisdom saving throw or become frightened 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 Greatwyrm's Frightful Presence for the next 24 hours.

Weakening Breath. The Greatwyrm exhales gas in a 90-foot cone. Each creature in that area must succeed on a DC 24 Strength saving throw or have disadvantage on Strength-based attack rolls, Strength checks, and Strength saving throws 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.

The Greatwyrm can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature's turn. The Greatwyrm regains spent legendary actions at the start of its turn.

Detect. The Greatwyrm makes a Wisdom (Perception) check.

Tail Attack. The Greatwyrm makes a tail attack.

Wing Attack (Costs 2 Actions). The Greatwyrm beats its wings. Each creature within 15 feet of the Greatwyrm must succeed on a DC 22 Dexterity saving throw or take 15 (2d6 + 8) bludgeoning damage and be knocked prone. The Greatwyrm can then fly up to half its flying speed.

The Greatwyrm can take mythic actions if it's undead fortitude has activated; choosing from the options below. Only one mythic action option can be used until the Greatwyrms is restored to at least 300 health.

Death Throes. The Greatwyrm reduces itself to 0 hit points, and its bones break down into a powder. Everything that inhales the powder must succeed on a DC 16 Constitution saving throw or become petrified. Any petrified creature can repeat this saving throw once, and if it fails, it cannot be undone by anything other than a Wish spell or a Greater restoration spell.

Ravaging Hunger. The greatwyrm attempts to swallow all creatures in the area, regardless of nature. Creatures targeted must succeed on a DC 10 Constitution saving throw or be swallowed. Any creature put into the Greatwyrm's ribcage in this way dissolves instantly; and the greatwyrm restores the total amount of hp the creatures consumed had.