I converted for my home campaign as I am running the pf1e Adventure Path – Reign of Winter.

YRAX, LORD OF THE HOWLING STORM

Level: 14
Large Dragon (Occult)
Perception: +26 (28 to Sense Motive); darkvision, scent (imprecise) 60 feet
Languages: Aklo, Aquan, Draconic, Triaxian, Common (Martian), Common (Terran); telepathy 100 feet
Skills: Acrobatics +24, Athletics +26, Deception +28, Diplomacy +28, Intimidation +26, Lore +28 (any one region or settlement), Occultism +26, Performance +28, Society +26, Stealth +24
Str: +6, Dex: +4, Con: +5, Int: +7, Wis: +8, Cha: +9

Defense

AC: 35
Fort: +23, Ref: +24, Will: +28; +2 status to all saves vs. occult
HP: 275
Immunities: controlled, paralyzed, sleep
Retract Body (reaction)
Trigger: The dragon is hit or critically hit by an attack made by a creature the dragon can see;
Effect: The dragon retracts the targeted body part or twists away to avoid the attack, gaining a +2 circumstance bonus to AC against the triggering attack.

Speed & Movement

Speed: 40 feet, climb 40 feet, fly 140 feet
Melee:

Jaws +28 (reach 10 feet), Damage 3d8+12 piercing
Claw +28 (agile, reach 10 feet), Damage 3d6+12 slashing
Tail +26 (reach 15 feet), Damage 2d10+12 bludgeoning

Ranged:

Mental Blast +28 (mental, range 100 feet), Damage 3d6+7 mental

Occult Innate Spells (DC 36):

7th: clairaudience, paralyze, veil of privacy
6th: calm, invisibility, paranoia
5th: bane, fear, phantom pain
4th: clairvoyance, honeyed words, suggestion
3rd: scouting eye, synaptic pulse, truespeech
2nd: daze, detect magic, figment, message, telekinetic projectile
1st: daze, detect magic, figment, message, telekinetic projectile

Special Abilities

Conjure Disguise (manipulate, occult, polymorph)
Frequency: once per day
Effect: Yrax conjures a perfect flesh-suit replica of a humanoid he’s seen, of his size or smaller, compressing himself into it, along with appropriate clothing. The process takes 1 minute, during which Yrax is off-guard. The transformation functions as Change Shape, but the disguise isn’t actively magical and doesn’t register as such. If Yrax is critically hit while in disguise, the suit explodes as per Detonate Disguise.

Detonate Disguise (occult)
Requirements: Yrax is wearing his conjured disguise.
Effect: Yrax erupts from the disguise, destroying it. Creatures within 5 feet take 13d6 bludgeoning damage (DC 34 basic Reflex save). A creature that fails its save is also dazzled for 1 round.

Rushed Transformation (three-actions) (concentrate, occult, manipulate, polymorph)
Frequency: once per hour
Effect: Yrax rapidly reshapes into a crude humanoid form, as per humanoid form but lasting only 1 minute and without the +4 status bonus to Deception.

Smoke Breath (two-actions) (occult, poison)
Yrax exhales a 50-foot cone of noxious smoke that deals 10d6 poison damage (DC 34 basic Fortitude save). The smoke remains for 1 minute, functioning as mist. Recharge: 1d4 rounds.

Sneak Attack: Yrax’s Strikes deal an additional 2d6 precision damage to off-guard targets.

Tactics

Before Combat:

Yrax casts clairaudience to spy on the party from a distance, assessing their strength and tactics.
He uses his conjure disguise ability to take the form of a humanoid, ideally one that won’t raise suspicion. He may attempt to engage the party in conversation or act as a neutral figure to lure them into a trap.

During Combat (Human Form):

In humanoid form, Yrax will begin by casting calm to suppress the party’s emotions and reduce the likelihood of a surprise attack.
He will use invisibility to maneuver and reposition, trying to get close to as many party members as possible.
If spotted, he uses phantom pain and fear to keep enemies at bay while casting paranoia on key spellcasters or ranged attackers, sowing distrust.
When the time is right (such as when enemies gather close), Yrax triggers Detonate Disguise to explode out of his humanoid form, dealing significant bludgeoning damage to nearby enemies. If enemies are clustered, this can maximize the damage and the dazzle effect.

After Transformation (Dragon Form):

After revealing his true form, Yrax will open with Smoke Breath to create an obscuring cloud that gives him cover while dealing poison damage. He will then use his mental blast from range to target low Will save enemies.
He may use suggestion on party members to try and break their cohesion, offering deceptive or self-serving instructions.
If the party closes in, Yrax will switch to melee, using his tail and jaws to deal high damage while keeping mobile with his flight speed.
He will save his more powerful offensive spells (paralyze, veil of privacy) for when the party is weakened, picking off individuals or disrupting their plans.

Morale:
Yrax is arrogant and overconfident, believing he can outwit and overpower the party. He will fight aggressively, preferring to toy with his enemies and demonstrate his superiority. However, if his health drops below 50%, he will consider retreating into the smoke and casting telekinetic projectile or clairvoyance to track the party while he regains his strength or waits for reinforcements.

Spell Description

Clairaudience: Allows Yrax to hear through a magical sensor at a distant location for 1 minute.
Paralyze: Paralyzes a creature for up to 4 rounds (DC 36 Fortitude), 3 actions to cast.
Veil of Privacy: Creates a 20-foot bubble that prevents eavesdropping and scrying, lasts 1 hour.
Calm: Removes emotional effects from a group of creatures, up to 10 creatures, for 10 minutes (2 actions).
Invisibility: Makes Yrax or an ally invisible for 10 minutes or until attacking.
Paranoia: Fills a target with paranoia, making them perceive all creatures as hostile.
Bane: Lowers attack rolls of enemies in an aura for 1 minute.
Fear: Frightens a creature, causing it to flee or become frightened 2 (DC 36 Will).
Phantom Pain: Inflicts mental and persistent damage over 1 minute (4d4 mental, average 10).
Clairvoyance: Lets Yrax see through a sensor in a distant location for 1 minute.
Honeyed Words: Gives Yrax a +4 status bonus on a Deception or Diplomacy check.
Suggestion: Compels a target to follow a reasonable request (DC 36 Will).
Scouting Eye: Summons an eye that scouts ahead for 10 minutes.
Synaptic Pulse: Deals 4d6 mental damage (average 14) and slows targets for 1 round (DC 36 Will).
Truespeech: Allows Yrax to understand and speak all languages for 10 minutes.
Daze: Deals 4 mental damage and can potentially stun a target (DC 36 Will).
Detect Magic: Reveals magical auras in a 30-foot cone.
Figment: Creates a minor illusion that lasts 1 minute.
Message: Allows Yrax to send a secret message to a nearby target.
Telekinetic Projectile: Hurls a small object at a target, dealing 2d6+7 bludgeoning damage (average 14).

Ivoryglass – The Lair of Yrax, Lord of the Howling Storm

Yrax’s lair, Ivoryglass, is a magnificent and eerie castle built entirely from glass and ice. Rising from the unforgiving desert sands of Barsoom, this structure is a testament to Yrax’s incredible power, defying the very nature of the arid landscape. The shimmering walls reflect the harsh sun, and at night, the entire castle glows faintly, casting strange reflections across the desert. The combination of smooth, translucent glass and glacial ice makes the castle a marvel of beauty and danger, as its slippery surfaces and dizzying heights are treacherous to even the most careful intruders.

Within Ivoryglass, Yrax controls the environment to his advantage, creating traps, illusions, and hazards that confound and disorient those who would dare to challenge him.

Optional Lair Actions

On initiative count 20 (losing initiative ties), Yrax can take one of the following lair actions. He can’t take the same action two rounds in a row:

Shattering Echo (sonic, mental): Yrax sends a wave of telepathic sound through the walls of Ivoryglass, disorienting his foes. Each creature within 120 feet that can hear must succeed on a DC 36 Will save or be stunned 1 until initiative count 20 of the next round. The harsh, shattering echo also causes any nearby glass structures to vibrate menacingly.
Prison of Ice (cold, evocation): Yrax conjures a block of magical ice around a creature within 60 feet, as per the wall of ice spell. The ice traps the creature unless it succeeds at a DC 36 Reflex save to escape before the wall forms. The ice lasts until the start of Yrax’s next turn or until the dragon uses this action again. Yrax uses his command over ice to punish intruders and control their movement within his lair.
Reflected Apparition (illusion): Yrax conjures a mirror image of himself in a different part of his lair. The illusion mimics his movements perfectly, as if the dragon is present in both places. The illusion lasts until initiative count 20 of the next round. Any creature interacting with the illusion must succeed on a DC 36 Will save to disbelieve, or they will be convinced that both Yrax and the illusion are real.

Yrax, Lord of the Howling Storm (pf2e)