Siege Crab (CR 14)

Gargantuan Vermin (Aquatic)
Alignment: Always neutral
Initiative: -2 (Dex); Senses: darkvision 60 ft.
Languages: cannot speak

AC: 37 (-4 size, -2 Dex, +23 natural, +10 deflection) touch 14, flat-footed 37
Hit Dice: 20d8+100 (190 hp); DR: 15/magic adamantine
Fort +25, Ref +12, Will +14
Speed: 60 ft., swim 60 ft.
Space: 20 ft./15 ft.
Base Attack +15; Grapple +37
Attack: Claw +21 melee
Full Attack: 4 claws +21 melee
Damage: Claw 2d6+10
Special Attacks/Actions: Constrict 2d6+10, improved grab, trample 2d6+15
Abilities: Str 30, Dex 6, Con 21, Int -, Wis 10, Cha 2
Special Qualities: Amphibious, force carapace, shielded compartment, vermin traits
Feats: Great Cleave; Power Attack
Skills: Swim +18
Advancement: 21-31 HD (Gargantuan); 32-60 HD (Colossal)
Climate/Terrain: Warm aquatic
Organization: Solitary
Treasure: None

Source: Monster Manual III

This massive crablike creature has four large pincers and six segmented legs. Its bright blue shell is covered with strange, glowing runes, and a round hatch is visible on the crustacean's underbelly.

The siege crab is a titanic crustacean that has been warped into a living amphibious war machine by powerful magic and skilled surgery. Kuo-toa clerics and wizards cooperated to first create them centuries ago, though reports exist of sahuagin and locathah warbands using siege crabs to raid surface settlements as well. Siege crabs are mutated from normal crabs in a process that takes decades. Each creature is magically bonded to a coral circlet, the wearer of which has absolute command over that siege crab and can give it direct verbal commands. The crab obeys these orders to the best of its ability, but unlike a construct it cannot be given conditional instructions or programs. The creature can only follow direct orders and is usually commanded to simply stand still if the controller needs to leave the crab's immediate vicinity.

A siege crab is almost 20 feet in diameter, stands 15 feet tall, and weighs over 30 tons. A siege crab does not speak but can understand simple instructions in any language given by the bearer of its coral circlet.

Aquatic Subtype

Creatures with the aquatic subtype always have swim speeds and thus can move in water without making Swim checks. An aquatic creature can breathe underwater. It cannot also breathe air unless it has the amphibious special quality.