Aspect of Null

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

Undying Wrath (Recharges after a Short or Long Rest). If the aspect would be reduced to 0 Hit Points, its current Hit Point total instead resets to 500 Hit Points, it recharges its Breath Weapon, and it 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 Null after its Undying Wrath activates. 

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

Bite. Melee Attack Roll: +19 to hit, reach 20 ft. Hit: 23 (2d12 + 10) Piercing damage plus 22 (4d10) Force damage.

Claw. Melee Attack Roll: +19 to hit, reach 15 ft. Hit: 21 (2d10 + 10) Slashing damage. If the target is a Huge or smaller creature, it has the Grappled condition (escape DC 20), and has the Restrained condition until this grapple ends. The aspect can have only one creature Grappled this way at a time. 

Tail. Melee Attack Roll: +19 to hit, reach 15 ft. Hit: 23 (2d12 + 10) Bludgeoning damage. If the target is a creature, it must make the following saving throw. Strength Saving Throw: DC 27. Failure: The target has the Prone condition. 

Time Breath (Recharge 5–6). Constitution Saving Throw: DC 26, each creature in a 300 foot cone. Failure:  66 (12d10) Force damage and is magically weakened as it is desynchronized from the time stream. While the creature is in this state, attack rolls against it have Advantage, it has the Poisoned condition, and other creatures have Resistance to all damage it deals. A weakened creature can repeat the saving throw at the end of each of its turns, ending the effect on itself after it succeeds on three of these saves. Failure: Half damage only. Nonmagical objects and vegetation in that area that aren’t being worn or carried crumble to dust. 

Time Gate (1/Day). The aspect conjures a 20-foot-diameter, circular portal in the space between its horns or in an unoccupied space it can see within 30 feet of itself. The portal links to a precise location on any plane of existence at a point in time up to 8,000 years from the present, whether past or future. The portal lasts for 24 hours or until the aspect's concentration ends (as if concentrating on a spell). The portal has a front and a back on each plane where it appears. Travel through the portal is possible only by moving through its front. Anything that does so is transported to the destination, appearing in the unoccupied space nearest to the portal. Deities and other planar rulers can prevent portals created by the aspect from opening in the rulers’ presence or anywhere within their domains.

Slow Time. Immediately after a creature the dragon can see ends its turn, the dragon targets a creature it can see within 90 feet of itself that is weakened by its Time Breath. Until the weakened effect ends on the target, its speed becomes 0, and its speed can’t increase.

Time Slip. The dragon halves the damage it takes from an attack made against it, provided it can see the attacker. The dragon can then immediately teleport, along with any equipment it is wearing or carrying, up to 60 feet to an unoccupied space it can see.

Legendary Action Uses: 3. Immediately after another creature’s turn, the aspect can expend a use to take one of the following actions. The aspect regains all expended uses at the start of each of its turns.

Attack. The aspect makes one Claw or Tail attack.

Furious Bite. The aspect makes one Bite attack. If the attack hits a creature, the target must make the following saving throw. Failure: The target has the Frightened condition until the end of the target's next turn. The aspect can’t take this action again until the start of its next turn.

If the aspect’s Undying Wrath trait has activated in the last hour, she can use the options below as legendary actions.

Death Shield. The aspect manifests an Avatar of Death for each hostile creature it is engaged with. These Avatars make a Reaping Scythe attack against each hostile creature and disappear immediately after. The aspect gains Temporary Hit Points equal to the damage dealt until the start of its next turn. The aspect can’t take this action again until the start of its next turn.

Necrotic Flare. Constitution Saving Throw: DC 26, each creature of the aspect's choice in a 60-foot Emanation originating from the aspect. Failure: 39 (6d12) Necrotic damage. Success: Half damage. Failure or Success: The aspect can’t take this action again until the start of its next turn.