Black Dracolich Greatwyrm

Stench. Any creature that starts its turn within 60 feet of the dracolich greatwyrm must succeed on a DC 26 Constitution saving throw or be poisoned until the start of the creature’s next turn. On a successful saving throw, the creature is immune to the stench for 1 hour.

Chromatic Awakening (Recharges after a Short or Long Rest). If the dracolich greatwyrm would be reduced to 0 hit points, its current hit point total instead resets to 425 hit points, it recharges its Breath Weapon, and it regains any expended uses of Legendary Resistance. Additionally, the dracolich greatwyrm can now use the options in the “Mythic Actions” section for 1 hour. Award a party an additional 105,000 XP (210,000 XP total) for defeating the dracolich greatwyrm after its Chromatic Awakening activates.

Spellcasting. Black Dracolich Greatwyrm is a 20th-level spellcaster. Their spellcasting ability is Intelligence (spell save DC 26, +18 to hit with spell attacks). They have the following wizard spells prepared:

Cantrips (at will): Chill Touch, Sapping Sting, Poison Spray, Ray of Frost, Toll the Dead

1st level (4 slots): Detect Magic, Magic Missile, Shield, Chaos Bolt

2nd level (3 slots): Blur, Enlarge/Reduce, Wither and Bloom, Acid Arrow

3rd level (3 slots): Counterspell, Fireball, Hold Person, Vampiric Touch, Slow

4th level (3 slots): Blight, Dimension Door, Shadow of Moil, Polymorph, Vitriolic Sphere

5th level (2 slots): Negative Energy Flood, Wall of Force

6th level (1 slot): Circle of Death, Disintegrate, Harm

7th level (1 slot): Prismatic Spray, Finger of Death, Teleport

8th level (1 slot): Control Weather, Maze, Power Word Stun

9th level (1 slot): Time Ravage

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

Undead Nature. The dracolich  greatwyrm doesn’t require food, drink or need to breath.

Multiattack. The greatwyrm makes one Bite attack and two Claw attacks.

Bite. Melee Weapon Attack: +18 to hit, reach 15 ft., one target. Hit: 21 (2d10 + 10) piercing damage plus 13 (2d12) force damage.

Claw. Melee Weapon Attack: +18 to hit, reach 10 ft., one target. Hit: 19 (2d8 + 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 greatwyrm can have only one creature grappled this way at a time.

Tail. Melee Weapon Attack: +18 to hit, reach 20 ft., one target. Hit: 19 (2d8 + 10) bludgeoning damage. If the target is a creature, it must succeed on a DC 26 Strength saving throw or be knocked prone.

Breath Weapon (Recharge 5–6). The greatwyrm exhales a blast of energy in a 300-foot cone. Each creature in that area must make a DC 26 Dexterity saving throw. On a failed save, the creature takes 40 (6d12) acid damage and takes 40 (6d12) necrotic damage. On a successful save, the creature takes half as much damage.

Change Shape. The greatwyrm magically transforms into any creature that is Medium or Small, while retaining its game statistics (other than its size). This transformation ends if the dragon is reduced to 0 hit points or uses its action to end it.

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.

Attack. The greatwyrm makes one Claw or Tail attack.

Wing Attack (Costs 2 Actions). The greatwyrm beats its wings. Each creature within 30 feet of it must succeed on a DC 26 Dexterity saving throw or take 17 (2d6 + 10) bludgeoning damage and be knocked prone. The greatwyrm can then fly up to half its flying speed.

Arcane Spear (Costs 3 Actions). The greatwyrm creates four spears of magical force. Each spear hits a creature of the greatwyrm’s choice it can see within 120 feet of it, dealing 12 (1d8 + 8) force damage to its target, then disappears.

If the greatwyrm’s Chromatic Awakening trait has activated in the last hour, it can use the options below as legendary actions.

Bite. The greatwyrm makes one Bite attack.

Chromatic Flare (Costs 2 Actions). The greatwyrm flares with elemental energy. Each creature in a 60-foot-radius sphere centered on the greatwyrm must succeed on a DC 26 Dexterity saving throw or take 14 (3d8) acid damage, and take 10 (2d8) necrotic damage.