This snake-like dragon has scales that shimmer with rainbow-colored light.

Rainbow Serpent (CR 20) XP 307,200
LG Colossal dragon (water) Init +12; Senses darkvision 120 ft., detect chaos, detect evil, detect magic, low-light vision, scent, true seeing; Perception +40
--- AC 36, touch 10, flat-footed 28 (+8 Dex, +26 natural, –8 size) hp 385 (22d12+242); regeneration 15 (epic) Fort +24, Ref +23, Will +20 Defensive Abilities freedom of movement, scintillating scales; DR 15/epic; Immune aging, mind-affecting effects, paralysis, poison, sleep, sonic; SR 31
--- Speed 40 ft., swim 80 ft.; swim the sky Melee bite +30 (3d8+16/19–20), tail +30 (3d6+16 plus grab) Space 30 ft.; Reach 30 ft. Special Attacks constrict (tail, 3d6+24), gaze Spell-Like Abilities (CL 20th; concentration +28)
Constant—detect chaos, detect evil, detect magic, true seeing
At will—dispel magic, haste, mark of justice, rainbow pattern (DC 22)
3/day—control water, dream, foresight, scintillating pattern
1/day—control weather, earthquake, move earth, time stop
--- Str 42, Dex 26, Con 32, Int 22, Wis 25, Cha 27 Base Atk +22; CMB +46 (+50 grapple); CMD 64 (can't be tripped) Feats Awesome Blow, Blind-Fight, Combat Reflexes, Improved Bull Rush, Improved Critical (bite), Improved Initiative, Improved Overrun, Improved Vital Strike, Lightning Reflexes, Power Attack, Vital Strike Skills Diplomacy +33, Knowledge (arcana, geography, history, nature, and religion) +31, Perception +32, Sense Motive +32, Spellcraft +31, Stealth +17, Survival +32, Swim +41 Languages Aquan, Auran, Celestial, Common, Draconic, Ignan, Sylvan, Terran
--- Environment any lake or river Organization solitary Treasure triple
--- Freedom of Movement (Ex) A rainbow serpent is under the constant effect of freedom of movement, as the spell of the same name. This effect cannot be dispelled. Gaze (Su) Dazed for 1d4+1 rounds, 30 feet, Will DC 29 negates. The save DC is Charisma-based. Scintillating Scales (Su) A rainbow serpent is cloaked in light. It sheds bright light within 30 feet of its space. Attacks against a rainbow serpent suffer a 50% miss chance, as if the serpent had total concealment. Creatures not relying on sight to not suffer this miss chance. Swim the Sky (Ex) A rainbow serpent can swim through the air as if it were water. While doing so, the rainbow serpent uses its normal swim speed, and counts as if it were swimming, not flying.

Rainbow serpents, named for their glimmering scales, are primordial dragons responsible for shaping the land when the world was young. Since that time, rainbow serpents have retired to the bottoms of lakes and rivers, where they spend most of their time slumbering. When a rainbow serpent awakens, it does so to battle chaos and evil in the vicinity of its watery lair. Preferred targets are individuals responsible for political strife, social upheaval, and the erosion of traditional values.

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