Leech, Giant (CR 1/3)

Small Vermin (Aquatic)
Alignment: Always neutral
Initiative: +1 (Dex); Senses: blindsight 10 ft. and scent

AC: 12 (+1 size, +1 Dex), touch 12, flat-footed 11
Hit Dice: 1d8 (4 hp)
Fort +2, Ref +1, Will -1
Speed: Swim 10 ft.
Space: 5 ft./5 ft.
Base Attack +0; Grapple -6
Attack: Bite +2 melee
Full Attack: Bite +2 melee
Damage: Bite 1 plus blood drain
Special Attacks/Actions: Anesthetize, attach, blood drain, disease
Abilities: Str 6, Dex 12, Con 11, Int -, Wis 8, Cha 2
Special Qualities: Vermin traits
Feats: Weapon Finesse
Skills: Hide +9 and Swim +6
Advancement: 2-3 HD (Small)
Climate/Terrain: Warm marsh
Organization: Colony (2-5) or swarm (6-11)
Treasure/Possessions: None

Source: Stormwrack

Anesthetize (Ex): A creature bitten by a giant leech must succeed on a Spot check (opposed by the giant leech's Hide check) to notice the attack if both the leech 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 leech, 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 without seeing it, notice the attack automatically.

Attach (Ex): If a giant leech hits with its bite attack, it uses its suckerlike mouth to latch onto the opponent's body. It deals no additional damage when it is attached, but it drains blood (see below). An attached leech loses its Dexterity bonus to AC and has an AC of 11.

An attached leech can be struck with a weapon or grappled itself. To remove an attached leech through grappling, the opponent must achieve a pin against the creature.

Blood Drain (Ex): A leech that is attached to its opponent deals 1 point of Constitution damage per round until it deals a total of 6 points, at which point it detaches from its target and swims off to digest its meal.

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

Skills: Giant leeches have a +4 racial bonus on Hide checks. A giant leech 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.

Giant leeches are found in murky water, where they can approach prey unseen. Characters might be attacked without even noticing.

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

Aquatic Subtype

Creatures with the aquatic subtype always have swim speeds and thus can move in water without making Swim checks. An aquatic creature can breathe underwater. It cannot also breathe air unless it has the amphibious special quality.