Dragon, Purple Ancient (CR 18)

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

AC: 39 (-4 size, +33 natural), touch 6, flat-footed 39
Hit Dice: 34d12+306 (527 hp); DR: 15/magic
Fort +28, Ref +19, Will +26
Speed: 40 ft., fly 200 ft. (clumsy), burrow 20 ft.
Space: 40 ft./15 ft.
Base Attack +34; Grapple +61
Attack: 1 bite +45, 2 claws +40, 2 wings +40, 1 tail slap +40, 1 crush +40, 1 tail sweep +40
Damage: 1 bite 4d6+15, 2 claws 2d8+7, 2 wings 2d6
Special Attacks/Actions: Breath weapon 20d10 (36)
Abilities: Str 41, Dex 10, Con 29, Int 26, Wis 25, Cha 34
Special Qualities: Night flier, Gust of wind, Pyrotechnics, Heat metal, Fire shield (fire form only), Suggestion, SR 29, Fear aura (DC 36)
Feats: #Feats: 12
Skills: Skill points: 278
Advancement: 35-36 HD (Gargantuan)
Climate/Terrain: Temperate plains
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: Triple Standard

Source: Dragon Compendium Vol. 1

Breath Weapon (Su): A purple dragon's breath weapon can take on three different forms. It can manifest as a cone of searing energy, a burst of blinding power, or a deadly blade of pure energy.

In its cone form, the purple dragon's breath weapon deals the listed damaged as normal. Creatures must make Reflex saves for half damage.

Purple Dragon SizeBurst Radius
Medium30 ft.
Large40 ft.
Huge60 ft.
Gargantuan80 ft.
Colossal100 ft.

In the breath weapon's final form, the dragon forms a blade of energy that it uses to slash through its enemies. The dragon uses the blade as a weapon within its normal melee reach. It gains iterative attacks with this weapon as per its base attack bonus, but never more than four such attacks. The blade ignores all physical barriers, allowing the dragon to make touch attacks to strike its foes. It deals half the damage listed for the dragon's breath weapon. Because of the energy nature of the blade, the dragon does not add its Strength modifier to the damage. The dragon makes this attack in addition to its other physical attacks, although it cannot use a bite attack in the same round it attacks with its blade. The blade dissipates at the end of the dragon's action.

Night Flier (Ex): The purple dragon's dark scales allow it to blend in with the night sky. While flying at night, it gains a +10 racial bonus on all Hide checks and ignores the standard size penalty on Hide checks.

Spell-Like Abilities: 3/day - gust of wind, pyrotechnics; heat metal; 1/day - fire shield; suggestion.