Crab Swarm Working Draft
Monstrous Crab, Tiny
 Tiny Vermin (Aquatic) 
Hit Dice: ½d8 (2 hp) 
Initiative: +0
Speed: 20 ft. (4 squares)
Armor Class: 16 (+2 size, +4 natural), touch 12, flat-footed 16
Base Attack/Grapple: +0/-6
Attack: Claw +2 melee (1d3-2) 
Full Attack: 2 claws +2 melee (1d3-2) 
Space/Reach: 2½ ft./0 ft.
Special Attacks: Constrict 2d3-2, improved grab 
Special Qualities: Amphibious, low-light vision, scent, vermin traits 
Saves: Fort +2, Ref +0, Will +0 
Abilities: Str 6, Dex 11, Con 10, Int —, Wis 11, Cha 2 
Skills: Hide +12, Spot +4 
Feats:  Weapon Finesse (B)
Environment: Temperate aquatic 
Organization: Colony (8–16)
Challenge Rating: 1/4
Treasure: None 
Alignment: Always neutral 
Advancement: —
Level Adjustment:  —
 Monstrous Crab, Diminutive
Diminutive Vermin (Aquatic) 
Hit Dice: ¼d8 (1 hp) 
Initiative: +0
Speed: 20 ft. (4 squares)
Armor Class: 16 (+4 size, +2 natural), touch 14, flat-footed 16
Base Attack/Grapple: +0/-11
Attack: Claw +4 melee (1d2-3) 
Full Attack: 2 claws +4 melee (1d2-3) 
Space/Reach: 1 ft./0 ft.
Special Attacks: Constrict 2d2-3, improved grab 
Special Qualities: Amphibious, low-light vision, scent, vermin traits 
Saves: Fort +2, Ref +0, Will +0 
Abilities: Str 4, Dex 11, Con 10, Int —, Wis 11, Cha 2 
Skills: Hide +16, Spot +4 
Feats: Weapon Finesse (B)
Environment: Temperate aquatic 
Organization: Colony (8–16)
Challenge Rating: 1/6
Treasure: None 
Alignment: Always neutral 
Advancement: —
Level Adjustment: —     
 Monstrous Crab Swarm, Tiny
  Tiny Vermin (Aquatic, Swarm) 
 Hit Dice: 4d8 (18 hp) 
 Initiative: +0
 Speed: 20 ft. (4 squares)
 Armor Class: 16 (+2 size, +4 natural), touch 12, flat-footed 16
 Base Attack/Grapple: +3/—
 Attack: Swarm (2d6)
 Full Attack: Swarm (2d6)
 Space/Reach: 10 ft./0 ft.
 Special Attacks: Clinging swarm, distraction
 Special Qualities: Amphibious, half damage from slashing and piercing, low-light vision, scent, swarm traits, vermin traits 
 Saves: Fort +4, Ref +1, Will +1
 Abilities: Str 6, Dex 11, Con 10, Int —, Wis 11, Cha 2 
 Skills: Hide +12, Spot +4 
 Feats: Weapon Finesse (B)
 Environment: Temperate aquatic 
 Organization: Solitary, scrabble (2-4 swarms), or horde (5-8 swarms)
 Challenge Rating: 2
 Treasure: None 
 Alignment: Always neutral 
 Advancement: —
 Level Adjustment: —
 Monstrous Crab Swarm, Diminutive
Diminutive Vermin (Aquatic, Swarm) 
  Hit Dice: 7d8 (31 hp)
  Initiative: +0
  Speed: 20 ft. (4 squares)
  Armor Class: 16 (+4 size, +2 natural), touch 14, flat-footed 16
  Base Attack/Grapple: +5/—
  Attack: Swarm (2d6)
  Full Attack: Swarm (2d6)
  Space/Reach: 10 ft./0 ft.
  Special Attacks: Clinging swarm, distraction
  Special Qualities: Amphibious, immune to weapon damage, low-light vision, scent, swarm traits, vermin traits 
  Saves: Fort +5, Ref +2, Will +2
Abilities: Str 6, Dex 11, Con 10, Int —, Wis 11, Cha 2 
  Skills: Hide +12, Spot +4 
  Feats: Weapon Finesse (B)
  Environment: Temperate aquatic 
  Organization: Solitary, scrabble (2-4 swarms), or horde (5-8 swarms)
  Challenge Rating: 3
  Treasure: None 
  Alignment: Always neutral 
  Advancement: —
  Level Adjustment: —
 A scuttling mass of saucer-sized crabs that clamber over each other in their eagerness to feed.
 
The hundreds of crabs that make up a crab swarm may be full grown  animals or the tiny young of larger monstrous crabs, which have  congregated into swarms after spawning. They are voracious scavengers  that will eat anything, living or dead, they come across.
 
  COMBAT
 
A giant crab swarm moves over anything that smells like food, then    attacks until either the swarm is dispersed or there's nothing left of    its opponents besides inedible scraps.     
 Clinging Swarm (Ex): Any living creature that takes damage from a  crab swarm's swarm attack must succeed at a Reflex  save (DC 13 for Diminutive crab swarms, DC 12 for Tiny) or 1d4 crabs from the swarm automatically grapple  the creature, dealing damage as usual. Treat these as individual monstrous crabs, which must be killed or grappled separately. The  Reflex save DC is Constitution-based.
Distraction (Ex): Any living creature that begins its turn with a crab swarm in its space must succeed on a Fortitude save (DC 13 for Diminutive crab swarms, DC 12 for Tiny) or be nauseated for 1 round. The save DC is Constitution-based.
 Skills: A monstrous crab has a +4 racial bonus on Hide and Spot checks.