Petrified Treant CR 9
(Variant) Mineral Warrior Treant
Huge Plant (Earth, extraplanar)
Init -1; Senses: Low-light vision, Darkvision 60' Listen +6, Spot +6
Languages Treant and Terran, sometimes Undercommon, Common, Dwarf, and/or Giant

AC 23 (-2 size, -1 Dex, +16 natural), touch 7, flat-footed 23
Hit Dice 7d8+35 (66 hp); DR 10/adamantine
Fort +12, Ref +3, Will +5

Speed 30 ft. (6 squares), burrow 15 ft.
Melee 2 slams +13 melee (2d6+10)
Ranged -
Base Atk +6; Grp +27
Space 15 ft.; Reach 15 ft.
Atk Options

Trample (Ex): 2d6+14 damage, Reflex DC 22 half. The save DC is Strength-based.
Earth Strike (Ex): Once per day, the fossilized treant can make an exceptionally vicious attack against any foe that stands on stone or earth. The mineral warrior adds its its Con bonus (usually +7) to its attack roll and deals extra damage (usually +7) equal to its racial hit dice.

Spell-like Abilities (CL 11):

Animate Earth (Sp): A fossilized treant in contact with soil or natural stone can animate the earth within 180 feet at will, controlling up to two masses of earth and stone at a time. It takes 1 full round for the earth hulks to form into vaguely animated shapes, under the treant's control. Thereafter it moves at a speed of 10 feet and fights as a huge earth elemental in all respects (save for the fact that the hulks are mindless, simply extensions of the treant's will). The hulks collapse into inert dirt and stone when they move out of range or the treant relinquishes control. This ability is used as a 6th-level spell. Summoned fossilized treants may not use this ability.

Str 30, Dex 8, Con 24, Int 10, Wis 14, Cha 10
SQ: Plant traits
Feats: Iron Will, Power Attack, Lightning Reflexes
Skills: Diplomacy +1, Hide -9*, Intimidate +4, Knowledge (nature) +4, Listen +6, Sense Motive +6, Spot +6, Survival +8

Treants have a +16 racial bonus on Hide checks made in forested areas in winter, areas with a significant number of dead trees, or in areas of natural stone.

Environment: Arctic forest, any mountain, or any underground
Alignment: Usually neutral
Advancement: 8-16 HD (Huge); 17-21 HD (Gargantuan)

A wizened, vaguely anthropomorphic tree towers over you. All its leaves are have long ago fallen, and its bark is a deep, fine-grained grey."

(Wizards of the Coast has an appropriate illustration in their art gallery.)

Fossilized treants are treants whose wood has been replaced with fine-grained stone. Despite the radical change in composition, this metamorphosis only serves to emphasize the most prominent traits of the treant: overwhelming power and methodical movement. Unfortunately, this transformation deprives the treant of its last vestige of both physical and mental flexibility; it's nearly impossible to deter a determined fossilized treant from its course of action, for good or ill.

While most fossilized treants are natives of the Earth Elemental Plane, occasionally a petrified treant corpse, old as the bones of the world, will spontaneously reawaken in mountainous or underground areas. (Such treants lack the Extraplanar subtype, will have much higher intelligence, and have all Knowledge skills as class skills.) Despite the move from the forests to rocky wastes or underground caverns, a fossilized treant will generally resume its role as a protector of nature, fighting those who despoil their new homes.

Fossilized treants may be summoned using Summon Monster VII or Summon Nature's Ally VII, at the option of the GM.

In combat, a fossilized treant is more aggressive than its younger counterparts, but still an intelligent combatant. Often, against smaller foes, it will hide and tie up foes with its earth hulks, and then trample both its foes and the replaceable hulks.