Monstrous Scorpion, Colossal (CR 12)

Colossal Vermin
Alignment: Always Neutral
Initiative: -1 (Dex); Senses: darkvision 60 ft., tremorsense 60 ft., and Spot +4

AC: 26 (-8 size, -1 Dex, +25 natural), touch 1, flat-footed 26
Hit Dice: 40d8+120 (300 hp)
Fort +25, Ref +12, Will +13
Speed: 50 ft.
Space: 40 ft./30 ft.
Base Attack +30; Grapple +58
Attack: Claw +32 melee
Full Attack: 2 claws +34 melee and sting +29 melee
Damage: Claw 2d8+12, sting 2d8+6 plus poison
Special Attacks/Actions: Improved grab, constrict 2d8+12, poison
Abilities: Str 35, Dex 8, Con 16, Int -, Wis 10, Cha 2
Special Qualities: Vermin
Feats: -
Skills: Climb +16, Hide -12, and Spot +4
Advancement: 41-60 HD (Huge)
Climate/Terrain: Warm desert
Organization: Solitary or colony (2-5)
Treasure: None

Source: Monster Manual

Monstrous scorpions are vicious predators that make unnerving scuttling noises as they speed across dungeon floors. A monstrous scorpion has a low, flat body: 80 feet long, 40 feet wide* and 10 feet high**.
*The number includes the scorpion's body and its legs; the actual body width is about a third of the total.
**The number indicates the height of the creature's body; the creature's stinger usually is held about as high off the ground as the creature is wide.