Alduin

Legendary Resistance (5/day). When Alduin fails a saving throw, he can choose to succeed instead.

Demigod's Ascendence (Recharges after a Short or Long Rest). If Alduin would be reduced to 0 hit points, his current his point total instead resets to 500 hit points, he recharges his Breath Weapon, and he regains any expended uses of Legendary Resistance. Additionally, the demigod can now use the options in the "Mythic Actions" section for 1 hour.

Multiattack. Alduin makes one Bite attack, one Claw attack, and one Tail attack.

Bite. Melee Weapon Attack: +19 to hit, reach 20 ft. Hit: (2d12+10) [Piercing] damage plus (4d10) [Force] damage.

Claw. Melee Weapon Attack: +19 to hit, reach 15 ft. Hit: (2d10+10) [Slashing] damage. If the target is a Huge or smaller creature, it is Grappled (escape DC 20) and is restrained until this grapple ends. Alduin can only have one creature grappled this way at a time.

Tail. Melee Weapon Attack: +19 to hit, reach 15 ft. Hit: (2d12+10) [Bludgeoning] damage. If the target is a creature, it must succeed on a DC 27 Strength saving throw or be knocked Prone.

Devourer's Flames. (Recharge 5-6) Alduin exhales devouring flames in a 300-foot cone. Each creature in that area must make a DC 27 dexterity saving throw. On a failed save, the creature takes (8d12) [fire] and (8d12) [radiant] damage. On a successful save, the creature takes half as much damage.

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

Attack. Alduin makes one Claw or Tail attack.

Furious Bite (costs 2 actions). Alduin makes one Bite attack. If the attack hits a creature, the target must succeed on a DC 27 Wisdom saving throw or become Frightened of Alduin until the end of its next turn.

Son of Time Itself (costs 2 actions). Alduin channels the energies of Akatosh, his father, summoning it as a barrier around himself. He immediately gains the benefits of the Haste spell until the end of his next turn, and does not suffer the penalties from it.

The Bell Tolls for Thee (costs 3 actions). Alduin flares with Divine energy. Each creature of his choice in a 60 ft. radius emanation must make a DC 27 Dexterity saving throw. On a failed save, the creature takes (6d12) [Force] damage. If the creature fails the saving throw by 10 or more, they are considered under the effects of the Slow spell until the start of Alduin's next turn. On a successful save, the creature takes half as much damage.