I found a scorched one conversion on the EN World Conversion Catalog. I think your version compares favourably.
Medium Undead (Fire)
Hit Dice: 7d12 (45 hp)
Speed: 30 ft. (6 squares)
Armor Class: 18 (+5 Dex, +3 natural), touch 15, flat-footed 13
Base Attack/Grapple: +3/+4
Attack: Touch +8 melee (1d8 fire plus dehydrating touch)
Full Attack: Touch +8 melee (1d8 fire plus dehydrating touch)
Space/Reach: 5 ft./5 ft.
Special Attacks: Dehydrating touch, insatiable thirst
Special Qualities: Damage reduction 5/magic, darkvision 60 ft., immunity to fire and spells with the light descriptor, rejuvenation, spell resistance 7, +4 turn resistance, undead traits, vulnerability to acid and cold, vulnerability to water
Saves: Fort +2, Ref +7, Will +5
Abilities: Str 12, Dex 21, Con —, Int 14, Wis 11, Cha 20
Skills: Bluff +15, Diplomacy +7, Disguise +15 (+17 acting), Intimidate +7, Listen +10, Search +12, Spot +10, Survival +13 (+15 following tracks)
Feats: Ability Focus (insatiable thirst), Skill Focus (Survival), Track, Weapon Finesse [B]
Environment: Warm deserts
Challenge Rating: 4
Alignment: Always neutral evil
Advancement: 8-20 HD (Medium)
Level Adjustment: —
A disheveled wanderer in tattered, weather-beaten garb stumbles through the sand beneath the hot desert sun. As it draws near, it appears extremely dehydrated and emaciated, its skin burnt and cracked.
Scorched ones arise from the remains of those who have succumbed to the perils of the desert. They now draw their power from the sun, wandering the deserts seeking out and tormenting the living. They often track caravans for many days, studying the strengths and weaknesses of their prey before the best opportunity arises to strike.
Due to their link to the power of the sun, scorched ones have weaker ties to the Negative Energy Plane than other undead.
A scorched one is 5 to 6 feet tall and weighs 100 to 200 pounds.
Scorched ones speak Common, Ignan, and Infernal in a hoarse, cracked voice.
A scorched one can be created with a create undead spell cast by a 15th-level spellcaster.
A scorched one prefers to rely on its potent supernatural and spell-like abilities, wading into melee only as an afterthought.
Dehydrating Touch (Su): The scorched one’s touch drains moisture from the body of living creatures, dealing 1d6 points of damage. This drain is especially devastating to water elementals and plant creatures, which instead take 1d8 points of damage.
Insatiable Thirst (Su): Twice per day as a standard action, a scorched one can create an insatiable thirst in one creature within 30 feet. The victim takes 2d6 points of nonlethal damage and becomes fatigued; the nonlethal damage and fatigue cannot be cured until the victim has drunk at least 2 quarts of liquid. In addition, the victim must succeed on a DC 20 Will save or be compelled to search for a liquid to drink. The victim will proceed to drink any liquid not known to be poisonous, including potions; this condition lasts for 10 minutes. This compulsion is a mind-affecting effect. The save DC is Charisma-based.
Rejuvenation (Su): In most cases, it’s difficult to destroy a scorched one through simple combat: The “destroyed” scorched one will reform in 24 hours. Even the most powerful spells are usually only temporary solutions. A scorched one that would otherwise be destroyed returns to its old haunts with a successful level check (1d20 + scorched one’s HD) against DC 16. The only way to completely destroy a scorched one is total immersion in water. Beheading a scorched one (either with a vorpal weapon or decapitation once it has been reduced to 0 hit points) renders it helpless until the next sunrise.
Spell-like Abilities (Sp): 2/day - light, scorching ray (2 rays, +8 ranged touch); 1/day - continual flame, fire seeds (acorn grenades only, +8 ranged touch, DC 21), searing light (+8 ranged touch). Caster level equals Hit Dice (7th for a typical scorched one). The save DCs are Charisma-based.
Vulnerability to Water (Ex): Scorched ones are particularly vulnerable to water, and contact with it (such as reaching into a pool or being splashed with a vial or bucket of water) inflicts 2d6 points of damage per strike. Complete immersion (including being caught in the rain or being subjected to a high volume of water, as from the geyser function of a decanter of endless water ) inflicts 6d6 points of damage per round.
Advanced Scorched Ones
A scorched one of 14 or more Hit Dice gains sunbeam as an additional spell-like ability, usable once per day. Caster level equals Hit Dice.
Upon reaching 14 Hit Dice, a scorched one’s damage reduction improves to 10/magic.
1999 Wizards of the Coast, Inc.
Originally found in Polyhedron Magazine #136 Scorched One