Ancient Devil Dragon

Legendary Resistance (4/Day, or 5/Day in Lair). If the dragon fails a saving throw, it can choose to succeed instead.

Spellcasting. The Ancient Devil Dragon is a 18th level spellcaster. Its spellcasting ability is CHR (spell save DC 26, +18 to hit with spell attacks). The Ancient Devil Dragon has following Sorcerer spells prepared:
Cantrips (at will): Soul Fire Bolt, Prestidigitation, Mending, Control Soul Flames, Create Soul fire Bonfire, Minor Illusion

1st level (4 slots): Shield, Absorb Elements, Silent Image, Charm Person

2nd level (3 slots): Soul fire Scorching Ray, Mirror Image, Soul fire Aganazzar's Scorcher

3rd level (3 slots): Counterspell, Soul Fireball, Major Image

4th level (3 slots): Soul Fire Shield, Wall of Soul Fire, Greater Invisibility

5th level (3 slots): Summon Draconic Spirit, Soul fire Immolation, Dominate Person

6th level (1 slot): True Seeing

7th level (1 slot): Soul Fire Storm

8th level (1 slot): Soul fire Incendiary Cloud

9th level (1 slot): Soul fire Meteor Swarm

Metamagic: 18 sorcerer points

Quickened Spell - When you cast a spell that has a casting time of 1 action, you can spend 2 sorcery points to change the casting time to 1 bonus action for this casting.

Twinned Spell - When you cast a spell that targets only one creature and doesn’t have a range of self, you can spend a number of sorcery points equal to the spell’s level to target a second creature in range with the same spell (1 sorcery point if the spell is a cantrip).

To be eligible, a spell must be incapable of targeting more than one creature at the spell’s current level. For example, magic missile and scorching ray aren’t eligible, but ray of frost is.

Subtle Spell - When you cast a spell, you can spend 1 sorcery point to cast it without any somatic or verbal components.

Multiattack. The dragon makes three Rend attacks. It can replace one attack per turn with a use of Spellcasting to cast any one of its spells.

Rend. Melee Attack Roll: +18, reach 15 ft. Hit: 19 (2d8 + 10) Slashing damage plus 10 (3d6) Soul Fire damage. (Damage is treated as fire for resistance purposes, but if a creature's hit points are reduced to 0 from an attack dealing Soulfire damage the soul of the creature hit with the attack has its soul sucked out and absorbed by this creature and becomes a random Fiend CR Rating = to current level or CR Rating or Lower under the control of the creature. This effect is permanent and can only be undone by a wish spell.)

Soul Fire Breath (Recharge 5–6). Dexterity Saving Throw: DC 26, each creature in a 90-foot Cone. Failure: 91 (26d6) Soul Fire damage. Success: Half damage. (Damage is treated as fire for resistance purposes, but if a creature's hit points are reduced to 0 from an attack dealing Soulfire damage the soul of the creature hit with the attack has its soul sucked out and absorbed by this creature and becomes a random Fiend CR Rating = to current level or CR Rating or Lower under the control of the creature. This effect is permanent and can only be undone by a wish spell.)

Quickened Spell

Shield, Absorb Elements, Counterspell

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature's turn, The dragon can expend a use to take one of the following actions. The dragon regains all expended uses at the start of each of its turns.

• 2 Actions: Soul Fireball. The dragon uses Spellcasting to cast Soul Fireball (level 4 version). The dragon can't take this action again until the start of its next turn.

• 1 Action: Soul Fire Rays. The dragon uses Spellcasting to cast Soul Fire Scorching Ray (level 3 version). The dragon can't take this action again until the start of its next turn.

• 1 Action: Pounce. The dragon moves up to half its Speed, and it makes one Rend attack.

Mythic Action Name. Enter the description for how mythic actions work for your monster here.

Mythic Action Name (Costs # Actions). Enter the description for your mythic action.