Dragon, Obsidian Great Wyrm (CR 25)

Gargantuan Dragon (Fire)
Alignment: Always neutral evil
Initiative: +0; Senses: blindsense 60 ft., darkvision120 ft., low-light vision, and keen senses
Languages: Draconic

AC: 45 (-4 size, +39 natural), touch 6, flat-footed 45
Hit Dice: 39d12+320 (580 hp); DR: 20/magic
Fort +30, Ref +22, Will +27
Speed: 40 ft., fly 200 ft. (clumsy), burrow 20 ft., swim 20 ft.
Space: 20 ft./15 ft. (20 ft. with bite)
Base Attack +39; Grapple +65
Attack: 1 bite +50, 2 claws +45, 2 wings +45, 1 tail slap +45, 1 crush +45, 1 tail sweep +45
Damage: 1 bite 4d6+14, 2 claws 2d8+7, 2 wings 2d6, 1 tail slap 2d8, 1 crush 4d6, 1 tail sweep 2d6
Special Attacks/Actions: Breath weapon 24d10 (38)
Abilities: Str 39, Dex 10, Con 27, Int 37, Wis 21, Cha 20
Special Qualities: Fire subtype, planar travel, Firefall, Biofeedback, burning ray, Whitefire, wall of ectoplasm, Ectoplasmic armor, flaming shroud, Plane shift, mind store, Genesis, SR 36, Fear aura (DC 35), Manifester level 19
Feats: #Feats: 14
Skills: Skill points: 513
Advancement: 41+ HD (Gargantuan)
Climate/Terrain: Inner Planes, warm mountains, underground
Organization: Solitary (1 dragon, any age), clutch (1d4+1 wyrmlings, very young, young, juvenile, or young adults), family (pair of mature adults and 1d4+1 offspring)
Treasure/Possessions: Double standard

Source: Web

Fire Subtype (Ex): An obsidian dragon is immune to fire but takes double damage from cold, except on a successful save.

Breath Weapon (Su): An obsidian dragon has one breath weapon: a cone of fire.

Planar Travel (Su): Obsidian dragons have the innate ability to pass instantly between the Material Plane and the Inner Planes, where they often make their homes.

Psionics (Sp): 3/day -- biofeedback, burning ray, ectoplasmic armor, firefall, flaming shroud, plane shift, wall of ectoplasm, whitefire; 1/day -- genesis, mind store. Manifester level varies by age; save DC d20 + appropriate ability modifier + power level.

Attack/Defense Modes: mind thrust/thought shield. An obsidian dragon manifests powers and gains additional attack and defense modes as if it were a psion with Metacreativity as its primary discipline.

Skills: An obsidian dragon has the Appraise skill for free at 1 rank per Hit Die.

Fire Subtype

A creature with the fire subtype has immunity to fire. It has vulnerability to cold, which means it takes half again as much (+50%) damage as normal from cold, regardless of whether a saving throw is allowed, or if the save is a success or failure.