Aspect of Sardior

Crystalline Eternity (Recharges after a Short or Long Rest). If the aspect would be reduced to 0 hit points, his current hit point total instead resets to 500 hit points, he recharges his Breath Weapon,  and he regains any expended uses of Legendary Resistance. Additionally, the aspect can now use the options in the "Mythic Actions" section for 1 hour. Award a party an additional 155,000 XP (310,000 XP total) for defeating the Aspect of Sardior after his Crystalline Eternity activates.

The Thanes' Sundering. The aspect can, at will, magically transform into 5 Greatwyrms; An Amethyst Greatwyrm named Aleithilithos, a Crystal Greatwyrm named Hrodel, an Emerald Greatwyrm named Smargad, a Sapphire Greatwyrm named Charsima, and a Topaz Greatwyrm named Tithonnas. If the aspect is killed, this ability activates automatically and cannot be stopped, and the Greatwyrms have triple disadvantage on all rolls.

Legendary Resistance (5/Day). If the aspect fails a saving throw, it can choose to succeed instead.

Multiattack. The aspect makes one Bite attack, one Claw attack, and one Tail attack..

Bite. Melee Weapon Attack: +19 to hit, reach 20 ft., one target. Hit: 22 (2d12 + 10) piercing damage plus 23 (5d8) force damage.

Claw. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 21 (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. The aspect can only have one creature grappled this way at a time.

Tail. Melee Weapon Attack: +19 to hit, reach 15 ft., one target. Hit: 23 (2d12 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 27 Strength saving throw or be knocked prone.

Breath Weapon (Recharge 5–6). The aspect uses one of the following breath weapons:

Breath-taking Blast. The aspect releases a wave of intense magical heat. All items made of light materials are instantly destroyed, leather is destroyed in 1d6 seconds, all non-metallic items are destroyed in 1d6+6 seconds, metallic items are destroyed in 1d6+12 seconds, and enchanted metallic items are destroyed in 1d6+18 seconds. Items with fire resistance take twice as long to be destroyed.

Breath Bejeweled. The aspect exhales gemstone powder of a type chosen by the aspect in a 300-­foot cone. Each creature in that cone must make a DC 27 Dexterity saving throw. On a failed save, the creature takes 38 (11d6) damage of 2 types of the aspect's choosing: Force, Necrotic, Psychic, Radiant, or Thunder. On a successful save, the creature takes half as much damage. After 1d4 rounds, the gemstone powder begins to grow gemstones of the powder's type at a rate of 1 cu. in. per 5 rounds, or at a rate of 1 cu. in. per 2 rounds in damp areas.

Change Shape. The aspect magically transforms into any Humanoid, Beast, or Gem Dragon, while retaining his game statistics (other than his size). This transformation ends if the aspect is reduced to 0 hit points or if he uses a bonus action to end it.

Psychic Step. The aspect teleports to an unoccupied space it can see within 90 ft. of it.

The dragon 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 dragon regains spent legendary actions at the start of its turn.

Attack. The aspect makes one Claw or Tail attack.

Furious Bite (Costs 2 Actions). The aspect 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 the aspect until the end of the target's next turn.

The aspect can take 3 Mythic actions, choosing from the options below. If the aspect's Crystalline Eternity trait has activated in the last hour, he can use the options below as legendary actions instead.

Breath Weapon (Recharge 5–6). The aspect uses one of the following breath weapons:

Incarnadine Exhalation (Costs 2 Actions). The aspect exhales a magical gas in a 350 ft. cone. Each creature in that cone must make a DC 28 Constitution saving throw. On a failed save, {[100-(Constitution Score+Constitution Modifier+1d20)]/2}% of the creature's blood is drawn to the surface, barely under the skin. On a successful save, the target may have {[75-(Constitution Score+Constitution Modifier+3d12)]/2}% or {[100-(Constitution Score+Constitution Modifier+1d20)]/4}% of their blood drawn to the surface. The blood displacement does not inherently cause any internal damage.

Exuberant Annihilation (Costs 3 Actions). The aspect exudes a 1-mile line of a light-absorbing substance from it's mouth that is 1-inch wide. The substance lingers for 5d20 rounds before dissipating. Each creature within 35 ft. of any point on the line that is not more than 5 feet in the air must make a DC [21+(creature's weight/100)] Strength saving throw. Creatures that are greater than 5 ft. in the air automatically fail this save. On a failed save, the creature is drawn {15-(creature's weight/50)] ft. (min. 0  ft.) closer to the nearest point on the line and is knocked prone. On a successful save, the creature is knocked prone until either the line disappears or the end of this round (min. 1) and is not affected by the line for the rest of this round (min. 1). When a creature is within 5 ft. of the line, they must also make a DC (30-creature's strength modifier) Constitution saving throw. On a save that was failed by 10 or more, the creature is ripped in half and dies. In [1d20-(CR or Level, whichever applies)] (min. 1) minutes, their spirit manifests within 200d6 ft. of the aspect as a ruby Draconic Shard. The Draconic Shard cannot take actions, cast spells, or move of its own accord, but it does retain all of its memories, abilities, spells, spell slots, and XP.