This is the crab I gave to my players. They were level 10-11 at the time.

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Mechanical crab:

Huge construct
AC: 20 (+15 natural (reinforced steel plates), -3 size, -2 dex)
Touch AC: 5
HP: 150 (DR 15/adamantine); at 50% see leaks

Immunities and resistances:
Resist fire 30/-: Fire damage over 30 is dealt to creatures within the MC as well.
Immune to lightning: Creatures inside the crab take 100% of lightning damage a crab would take
Resist acid 20/-
Immune to cold

STR 35
DEX 6
CON -
INT -
WIS -
CHA -

BaB: +9
Grapple: +29


Movement modes:
It takes 1 person to drive the MC. While underwater it has two choices.
a) It can move at a speed of 100 ft, but it can't attack and its manuverability is treated as clumsy.
b) Speed 40 ft, can attack and manuverability is treated as good.

On land it moves slowly (15 ft) but can attack. On land it can't charge or run.
It is not known how deep can a MC go. It has been tested to up to 500 ft.


Attack modes:
It takes 1 person to man the MCs defensive modes. The following options are avaible to him:
a) A claw attack. Reach 10. +19 to hit, 2d6 + 12 damage. Standard action. Can be used in grapple.
b) A tail slap. Reach 15. +19 to hit. 3d6+18 damage. Full round action.
c) 2 claw attacks as above, but with bonuses +17/+17 . Full round action. Can be used in grapple.
d) Lightning surge. All creatures within 30 ft of the crab take 8d6 lightning damage (refl 18 half, creatures with metal weapons or armor take a -4 penalty to save). 1 round action. Can be used in grapple.
e) Escape a grapple. Make a grapple attemp with +29 bonus to leave the grapple (or to resist). Standard action or no action.


While in combat the MC is limited as any creature to actions it can take, however it requires at least 2 operators to both fight and move during the same round.

Saves: As a inanimate object it automatically fails all reflex saves. It is immune to all effects requiring will saves. It makes fort saves only against effects that would affect objects at a +16 bonus. It is considered to be a attended object for purposes of spells.

The MC resembles a huge lobster, and it takes a spot DC 25 to tell otherwise. The enterance to the aparatus is in the rear, near the tail. The enterance hatch does not need to be closed up to 100 ft in depth, as the air pressure keeps the water from coming in. At depths greater then those water begins pouring in. The MC provides its occupants a constant air supply enough for 6 medium sized persons. Aside from cramped space for 6 medium sized persons, there is enough storage for about 2000 lbs of gear. If the MC is loaded with more then 4000 lbs of gear and creatures it can not rise to the surface and will sink slowly. On its head there are two large dome shapped glass view ports that allow the driver and weapon controler view of their surroundings. There are also numerous viewports around and on the bottom of the MC. However visibility is still limited, the driver and the weapon operator take a -4 to their spot checks, while the rest of the passengers take a -10 penalty. The interior can be lit with a dim red light that is almost undetectable from outside, or be brightly lit.

The MC also has a modifiable outside lamp, that can shed bright illumination up to 60 ft.


Leaks: If the MC takes 75 damage, it develops leaks. Water keeps coming in and floods the interior in 4 hours rendering the MC inoperable.
If the MC takes 120 damage, its speed is reduced by 50%, and fills up with water in 2 hours.
If the MC is destroyed, the creatures inside take 6d6 damage and are ejected in random places outside the MC.

A destroyed MC cannot be repaired, while a damaged one can, with spells, or a DC 20 blacksmithing check each day repairs 1d8+1 points of damage.