Swarm

Some aquatic creatures present a negligible threat by themselves, but in the presence of hundreds or thousands of their kind they become terrifying predators.

Swarm Traits: Swarms are masses of Fine, Diminutive, or Tiny creatures that would not be particularly dangerous in small groups, but can be terrible foes when gathered in sufficient numbers. While a single jellyfish swarm might actually be hundreds of feet across, for game purposes a swarm is defined as a single creature with a space of 10 feet⁠—​gigantic schools of piranhas are actually composed of dozens of swarms in close proximity. A swarm has a single pool of Hit Dice and hit points, a single initiative modifier, a single speed, and a single Armor Class. It makes saving throws as a single creature.

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.

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).

Jellyfish Swarm

This patch of water shines like mother-of-pearl. Tiny, clearbodied jellyfish, almost invisible in the water, drift beneath the surface.

A jellyfish swarm drifts with the ocean currents. Its myriad creatures trail poisonous tentacles that can stop a creature in its tracks. This swarm depicts a particularly toxic kind of jellyfish, such as the box jelly.

Individual jellyfish in the swarm are a few inches long and nearly transparent.

Combat

A jellyfish swarm deals no combat damage, but its poison is potent. Once a creature is reduced to 0 Dexterity, it typically drowns in short order and the colony feeds on its decaying corpse, which is carried about within the swarm’s mass.

Distraction (Ex): Any living creature vulnerable to the jellyfish swarm’s damage that begins its turn with a swarm in its square is nauseated for 1 round; a DC 16 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.

Poison (Ex): Injury, Fortitude DC 18, 1d8 Dex/1d8 Dex. The save DC is Constitution-based and includes a +2 racial bonus. A creature that fails either Fortitude save is also stunned for 1 round.

Tremorsense (Ex): A jellyfish swarm can detect and pinpoint any creature in the water within 30 feet.

Skills: A jellyfish swarm has a +8 racial bonus on Hide due to its near transparency.

A jellyfish swarm has a +8 racial bonus on any Swim check to perform some 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.

Source: Stormwrack, page 161.

Leech Swarm

The water squirms with uncounted thumb-sized sluglike creatures, each one wriggling in an unsettling manner.

Leeches are found in murky water, where they can approach prey unseen.

Combat

A leech swarm relies on stealth and blood drain to quietly disable its target. An unobservant creature can be drained dry without even realizing the cause of its weakness.

(DM Tip: Take note of the PCs’ Spot checks and AC before running an encounter with a leech swarm. Record damage dealt by undetected leeches, but do not inform the player of the damage until his or her character notices the attack.)

Anesthetize (Ex): A creature attacked by a leech swarm must succeed on a Spot check (opposed by the swarm’s Hide check) to notice the attack if both the leech swarm and its target are in murky water at least 2 feet deep. Each round of blood drain entitles the creature to another Spot check to notice the leeches, with a cumulative +2 bonus on the check per round after the first. Characters attacked in clear water, or who have some means of detecting the leech swarm without seeing it, notice the attack automatically.

Blood Drain (Ex): Any living creature damaged by a leech swarm also takes 1 point of Constitution damage as the swarm drains its blood. This damage repeats every round thereafter unless the creature successfully exits the swarm and spends a full-round action removing leeches from its body.

Disease (Ex): A creature damaged by a leech swarm must succeed on a DC 15 Fortitude save or contract red ache.

Distraction (Ex): Any living creature vulnerable to the leech swarm’s damage who notices the swarm and begins its turn with a swarm in its square is nauseated for 1 round; a DC 10 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.

Skills: A leech 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.

Source: Stormwrack, page 162.

Piranha Swarm

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.

Combat

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.

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.

Source: Stormwrack, page 162.