Primordial Colossus (CR 18)

Colossal Construct
Alignment: Always neutral
Initiative: +0
Languages: Cannot speak

AC: 31 (-8 size, -3 Dex, +32 natural), touch -1, flat-footed 31
Hit Dice: 54d10+80 (297 hp); DR: 15/-
Fort +19, Ref +15, Will +18
Speed: 60 ft. or 60 ft. fly (clumsy) or 60 ft. swim
Space: 50 ft./50 ft. (300 ft. tall)
Base Attack +40; Grapple +75
Attack: Slam +51 melee
Full Attack: 2 slams +51 melee
Damage: Slam 4d8+19
Special Attacks/Actions: Death drop, stomp
Abilities: Str 48, Dex 5, Con -, Int -, Wis 10, Cha 5
Special Qualities: Air armor, construct traits, immunity to magic, impassive, thunderous step
Feats: -
Skills: -
Advancement: 55-70 HD (Colossal)
Climate/Terrain: Any
Organization: Solitary
Treasure/Possessions: None

Source: Dragon #336

Death Drop (Ex): If a flying or walking primordial colossus is reduced to 0 bit points it falls to the ground in a gigantic pile, much like an avalanche. All creatures within 20 feet of the colossus when it is destroyed are effectively within the bury zone of the falling debris and take 8d6 points of damage, half that amount if they succeed at a DC 15 Reflex save, and are buried. Buried creatures take damage and can be rescued as detailed in chapter 8 of the DMG. Creatures within 80 feet of the crumbling colossus are in the slide zone and must make a DC 15 Reflex save or take 3d6 points of damage.

Stomp (Ex): By concentrating all its energy on one full-round attack, a walking primordial colossus may stomp upon any foe of less than Colossal size within its threatened area. This attack is treated as a single slam attack that, if it succeeds, is treated as though the primordial colossus had made and succeeded at a grapple check. For every round this grapple is maintained the colossus may deal slam damage to the target as a free action. The target may attempt to escape the grapple every round as normal. Unless the target escapes, this grapple lasts until the colossus moves or decides to release the target. While using this ability a primordial colossus is not considered grappled and still threatens the area surrounding it.

Air Armor (Su): Constructed from all the elements, a column of strong winds surrounds flying and walking primordial colossi at a radius of 30 feet. Strong wind imposes a -2 penalty on ranged attack rolls and Listen checks, as well as knocks down Tiny or smaller creatures.

Immunity to Magic (Ex): A primordial colossus is immune to any spell or spell-like ability that allows spell resistance.

Impassive (Ex): A primordial colossus will only attack a creature that purposefully deals damage to it first. Creatures daring to approach a primordial colossus can make a DC 20 Climb check. If successful, the creature is capable of grabbing hold of the colossus and riding upon it. If the primordial colossus is stationary when this check is made there is no penalty for failure. However, if the primordial colossus is moving when a creature attempts and fails its Climb check, it is dealt damage equal to the colossus's slam ability.

Thunderous Step (Ex): All creatures smaller than Colossal within 60 feet of a walking primordial colossus when it moves must succeed at a DC 15 Balance check or fall prone.

Rarely purposefully attacking other creatures, the mere passage of a primordial colossus can be a ruinous event. When they do attack, however, these massive constructs lack the intellect to form complex plans, but few tactics could prove more effective than a blow from a primordial colossus's gigantic limbs.