Giant crabs behave much like their smaller cousins, feeding on both plant material like algae and fungus and animal matter such as fish, seabirds, and even unwary humanoids. The coloration of a giant crab's hard exoskeleton varies widely depending on species, and over time even shifts in response to its diet.
Other species of giant crab exist as well, some smaller but most quite a bit larger. You can adjust the stats given here by changing Hit Dice and size (changing Strength, Dexterity, and Constitution as appropriate) to represent a wide range of different species of giant crab. The following table lists the most common variants.
| Species | CR | Size | HD |
|---|
| King crab | 1/4 | Tiny | 1d8 |
| Coconut crab | 1/2 | Small | 1d8 |
| Rock crab | 4 | Large | 5d8 |
| Shark-eating crab | 7 | Huge | 8d8 |
| Great reef crab | 10 | Gargantuan | 11d8 |
| Shipwrecker crab | 13 | Colossal | 14d8 |
Water Dependency — Giant crabs can survive out of the water for 1 hour per point of Constitution. Beyond this limit, a giant crab runs the risk of suffocation, as if it were drowning.
Grab
(claws)
Ex
from Universal Monster Rule
If a creature with this special attack hits with the indicated attack (usually a claw or bite attack), it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity. The creature has the option to conduct the grapple normally, or simply to use the part of its body it used in the grab to hold the opponent. If it chooses to do the latter, it takes a –20 penalty on its combat maneuver check to make and maintain the grapple, but does not gain the grappled condition itself. A successful hold does not deal any extra damage unless the creature also has the constrict special attack. If the creature does not constrict, each successful grapple check it makes during successive rounds automatically deals the damage indicated for the attack that established the hold. Otherwise, it deals constriction damage as well (the amount is given in the creature's descriptive text). Creatures with grab receive a +4 bonus on combat maneuver checks made to start and maintain a grapple. Unless otherwise noted, grab works only against opponents no larger than the same size category as the creature. If the creature can use grab on sizes other than the default, this is noted in the creature's Special Attacks line.
Constrict
(1d4+2)
Ex
from Universal Monster Rule
A creature with this special attack can crush an opponent, dealing bludgeoning damage, when it makes a successful grapple check (in addition to any other effects caused by a successful check, including additional damage). The amount of damage is given in the creature's entry and is typically equal to the amount of damage caused by the creature's melee attack.