Creature: The Great Earth Serpents (CR 20)

Great Earth Serpent CR 20

neutral Colossal Magical Beast (fire)
Init: +3 Senses: Tremmorsense: 60 ft, 5 x lowlight vision
Listen +1 Spot +26

AC: 31 (-8 size, +3 dex, +20 natural)
HP: 267 (HD 25d10 + 125)
Immune: fire
Fort: +17 Ref: +15 Will: +9
Weakness: cold

MV: 30 ft, burrow 20ft, swim 60ft
Attack: +38 bite 2d8 + 15 plus 2d8 fire or +37 tail slap 4d6 + 22 plus 2d8 fire
Full Attack: +38 bite 2d8 + 15 plus 2d8 fire and +32 tail slap 4d6 + 22 plus 2d8 fire
Atk Options: constrict, improved grab, swallow whole
Space / Reach: 30' / 20'
Base Attack: +37 Grapple: +51

Abilities: Str: 41 Dex: 17 Con: 21 Int: 5 Wis: 12 Cha: 3
SQ: DR 10/frost, destroy weapon, fire immunity, heat aura, sheds light 20'
SA: constrict, improved grab, swallow whole
Feats: Power Attack, Cleave, Great Cleave, Awesome Blow, Improved Sunder, Snatch, Weapon Focus (bite), Improved Bull Rush, Iron Will.
Skills: spot 25+1 = +26

Treasure: double standard, no items (as raw precious metal and uncut gems - see bolow)

A colossal serpent rears up 20 feet out of the lava, it's body composed of molten rock and it eyes shining with white-hot light. The great heat of it's body distorts the air.

Earth serpents, the beasts that dwell beneath and among the mountain's roots and are the cause of earthquakes and volcanoes (according to dwarves), appear to be colossal snakes or wyrms whose bodies are composed of lava or semi-molten rock, and have eyes that gleam with a white-hot light. Dwelling in and around the lakes of molten stone that pepper the underdark and delving deeper even than dwarven lore, these creatures are mysterious and strange.

Generally content to bask in the pools of lava that their bodies create, sometimes they are seized with a sudden restlessness, burrowing through solid rock and sometimes causing disastrous shifts in the surface.

Great earth serpents are rumored by deep dwarves to have blood of molten gold, and when they die create veins of ore.

COMBAT
Great Earth Serpents are straightforward in combat, charging, swallowing and crushing any that intrude on their territory, or threaten them or their offspring.

Damage Reduction: No weapon without the magical frost ability has a chance of completely penetrating the molten metal and rock that compose an earth serpent's scales.

Destroy Weapon (Su): Any nonmagical weapon that strikes them is destroyed by the great heat of their bodies.

Fire Trait: Great earth serpents take no damage from fire at all, and take double damage from cold except on a successful save.

Improved Grab (Ex): To use this ability, a great earth serpent must hit with its bite or tail attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, it establishes a hold and can attempt to swallow the foe or constrict the following round.

Swallow Whole (Ex): A great earth serpent can try to swallow a grabbed opponent of a smaller size than itself by making a successful grapple check. Once inside, the opponent takes 4d8+22 points of crushing damage plus 2d8 points of heat damage per round from the serpent's gizzard. A swallowed creature can cut its way out by using a light slashing or piercing weapon to deal 25 points of damage to the gizzard (AC 24). Once the creature exits, muscular action closes the hole; another swallowed opponent must cut its own way out. A Colossal serpent’s interior can hold 4 Large, 16 Medium, 64 Small, 256 Tiny, or 1024 Diminutive or smaller opponents.

Constrict (Ex): A great earth serpent automatically deals 4d6+22 points of bludgeoning and 2d8 heat damage with a successful grapple check.

Heat Aura (Su): All creatures and objects within 10' of an earth serpent take 2d8 damage from the immense heat of their bodies, (reflex save ½). Those failing their saves have caught fire and will burn for an additional 1d4 rounds for 1d6 points of damage per round.

Tremmorsense: Great Earth Serpents have tremorsense to a distance of 60 ft.

Lowlight vision: Great Earth Serpents can see 5 times as far as a normal human in low light.

Sheds light: Great Earth Serpents shed light in a 20' radius.

Hide: Great Earth Serpents gain a +10 to hide checks when in lava.

Treasure: Earth serpents have significant quantities of molten precious metal in their bloodstreams and gems in their eyes and skulls. After their deaths the metals cool and can be mined from the rocklike flesh. Roll for coins and gems and award that value in raw ore by dividing the coin value by 50 to determine the number of pounds of precious metal available.