Piranha Swarm (CR 4)
AC: 15 (+2 size, +2 Dex, +1 natural), touch 14, flat-footed 13
Hit Dice: 8d8+11 (47 hp)
Fort +7, Ref +8, Will +3
Speed: Swim 40 ft.
Space: 10 ft./0 ft.
Base Attack +6; Grapple -
Full Attack: Swarm
Damage: Swarm 3d6
Special Attacks: Distraction
Abilities: Str 4, Dex 15, Con 12, Int 1, Wis 12, Cha 2
Special Qualities: Half damage from slashing and piercing weapons, swarm traits
Feats: Alertness; Improved Initiative; Toughness
Skills: Hide +10, Listen +9, Spot +8, and Swim +5
Climate/Terrain: Warm aquatic
Organization: Solitary or school (2-4 swarms)
The water boils with small, darting fish, each armed with a jawful of razor-sharp teeth.
One of the most feared denizens of warm aquatic environments is the piranha swarm, capable of devouring even a large creature with amazing quickness.
Due to a piranha's unusually strong jaws and sharp teeth, piranha swarms deal more damage than a swarm of their Hit Dice normally would.
Distraction (Ex): Any living creature vulnerable to the piranha swarm's damage that begins its turn with a swarm in its square is nauseated for 1 round; a DC 15 Fortitude save negates the effect. Even with a successful save, spellcasting or concentrating on spells within the area of a swarm requires a Concentration check (DC 20 + spell level). Using skills requiring patience and concentration requires a DC 20 Concentration check. The save DC is Constitution-based.
Swarm Traits: A swarm has no clear front or back and no discernible anatomy, so it is not subject to critical hits or flanking. A swarm made up of Tiny creatures takes half damage from slashing and piercing weapons. A swarm composed of Fine or Diminutive creatures is immune to all weapon damage. A swarm of Tiny creatures consists of 1,000 creatures. A swarm of Diminutive creatures consists of 5,000 creatures. A swarm of Fine creatures consists of 10,000 creatures. Larger swarms are represented by multiples of single swarms. A large swarm is completely shapeable, though it usually remains contiguous.
Reducing a swarm to 0 hit points or fewer causes the swarm to break up, though damage taken until that point does not degrade its ability to attack or resist attack. Swarms are never staggered or reduced to a dying state by damage. Also, they cannot be tripped, grappled, or bull rushed, and they cannot grapple another.
A swarm is immune to any spell or effect that targets a specific number of creatures (including single-target spells such as disintegrate), with the exception of mind-affecting effects if the swarm has an Intelligence score and a hive mind. A swarm takes a -10 penalty on saving throws against spells or effects that affect an area, such as many evocation spells or grenadelike weapons. If the area attack does not allow a saving throw, a swarm takes double damage instead.
The aquatic swarms presented here are susceptible to vigorous or stronger currents, such as that created by a control currents spell. For purposes of determining the effects of currents on a swarm, treat the swarm as a creature of the same size as its constituent creatures. Current effects deal 1d4 points of nonlethal damage to the swarm per spell level (or Hit Die of the originating creature, in the case of effects such as a water elemental's vortex). A swarm that takes subdual damage sufficient to exceed its current hit points becomes disorganized and dispersed, and does not re-form until its current hit points exceed its subdual damage.
Skills: A piranha swarm has a +8 racial bonus on any Swim check to perform a special action or avoid a hazard. It can always choose to take 10 on a Swim check, even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line.