Encounters: Cormyrean Marshes - The Vast Swamp
Leech Swarm (CR 1)
AC: 18 (+8 size), touch 18, flat-footed 18
Hit Dice: 2d8-2 (7 hp)
Fort +2, Ref +0, Will +1
Speed: Swim 10 ft.
Space: 10 ft./0 ft.
Base Attack +1; Grapple -
Full Attack: Swarm
Damage: Swarm 1d6 plus blood drain
Special Attacks: Anesthetize, blood drain, disease, distraction
Abilities: Str 1, Dex 11, Con 8, Int -, Wis 12, Cha 2
Special Qualities: Immune to weapon damage, swarm traits
Skills: Hide +16 and Swim +3
Climate/Terrain: Warm marsh
Organization: Solitary or plague (2-4 swarms)
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.
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 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.
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.)