Ooze, Obsidian (CR 9)
AC: 19 (-1 size, -5 Dex, +15 natural), touch 4, flat-footed 19
Hit Dice: 12d10+60 (126 hp)
Fort +9, Ref -1, Will -1
Speed: 20 ft., burrow 20 ft.
Space: 10 ft./5 ft.
Base Attack +9; Grapple +18
Attack: Spine +13 melee (1d8+5/15-20 plus 1d6 fire)
Full Attack: 3 spines +13 melee (1d8+5/15-20 plus 1d6 fire)
Special Attacks/Actions: Engulf, improved grab, skewer
Abilities: Str 20, Dex 1, Con 20, Int -, Wis 1, Cha 1
Special Qualities: immunity to fire and piercing and slashing weapons, molten core, ooze traits, vulnerability to cold
Feats: Improved Critical (spine)[B]
Advancement: 13-16 HD (Large), 17-26 HD (Huge), 27-36 HD (Gargantuan), 37+ HD (Colossal)
Climate/Terrain: Underground (volcanoes)
Engulf (Ex): As a standard action, an obsidian ooze can engulf any creature that it is currently grappling or being grappled by it. Once a creature is engulfed, the creature takes 4d6 points of fire damage per round from the ooze's molten interior. An engulfed creature can try to pound its way out with any natural or light bludgeoning weapons. Dealing a total of at least 30 points of damage to the interior of the ooze (AC 15) in this way creates an opening large enough to permit escape, but causes the molten interior to spill out in a 5-foot radius. All creatures in this range take 2d6 points of fire damage, or half on a successful Reflex save (DC 21). Once a single engulfed creature exits, the hole quickly hardens over; thus, another engulfed opponent must pound its own way out. An obsidian ooze can hold 2 Medium or 8 Small or smaller opponents. The save DC is Constitution-based.
Improved Grab (Ex): If an obsidian ooze hits an opponent that is at least one size category smaller than itself with a spine attack, it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity.
Sharp Spines (Ex): An obsidian ooze's spines have a critical threat range of 18-20, which the creature's Improved Critical feat increases to 15-20.
Molten Core (Ex): Piercing and slashing weapons deal no damage on a successful hit to an obsidian ooze, but they do have a chance of being damaged by the creature. Any weapon that inflicts damage to an obsidian ooze must make a Reflex saving throw (DC 21) or take 4d6 points of fire damage. If the weapon was a natural weapon, the attacking creature suffers this damage. The save DC is Constitution- based. Worse, the attack causes the creature's lava-like core to spray out in a gout. The attacking creature takes 2d6 points of fire damage, or half on a successful Reflex save (DC 21). The save DC is Constitution-based.
An obsidian ooze coils like a snake when it locates prey but it does not strike when it attacks. Rather, it grows long lances of razor-sharp but flexible obsidian spines with shocking speed, skewers creatures in range, and then flows up these spines to engulf captured prey.
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.