Blackskate (CR 4)

Large Undead (Aquatic)
Alignment: Always neutral evil
Initiative: +3 (Dex); Senses: darkvision 60 ft., scent, Listen +4, and Spot +4

AC: 18 (+3 Dex, +6 natural, -1 size), touch 12, flat-footed 15
Hit Dice: 4d12 (26 hp); DR: 5/slashing
Fort +1, Ref +4, Will +5
Speed: Swim 40 ft.
Space: 10 ft./5 ft.
Base Attack +2; Grapple +11
Attack: Stinger +6 melee
Full Attack: Stinger +6 melee and bite +1 melee
Damage: Stinger 1d6+2 plus poison, bite 1d8+5
Special Attacks/Actions: Blood rage, poison
Abilities: Str 20, Dex 17, Con -, Int 12, Wis 12, Cha 16
Special Qualities: Blood tracker, scent, undead traits
Feats: Stealthy; Swim-By Attack
Skills: Escape Artist +5, Hide +8 (+12 on seafloor), Listen +4, Move Silently +12, Search +4, Spot +4, Survival +8, and Swim +16
Advancement: 5-12 HD (Large)
Climate/Terrain: Any aquatic
Organization: Solitary or pair
Treasure/Possessions: None

Source: Stormwrack

Blood Rage (Ex): A blackskate that begins its turn within 30 feet of a living, wounded creature can enter a blood rage. It thrashes back and forth with tremendous power, gaining a +2 bonus on attack and damage rolls and +2 dodge bonus to AC. The blood rage lasts for a number of rounds equal to 3 + the blackskate's Charisma modifier (normally 6 rounds total). It can enter a blood rage once per day.

Poison (Ex): A blackskate's venomous stinger is capable of administering a necrotic poison that causes flesh to quickly wither and slough off. Injury, Fortitude DC 15, 1d6 Con/1d6 Con. The save DC is Charisma-based.

Blood Tracker (Su): A blackskate is capable of tracking anyone whose blood it has tasted (that is, anyone whose blood has been shed near it in the water). It can follow any such trail infallibly, as long as its quarry remains in the same body of water as the blackskate. It succeeds automatically, unless the quarry uses some magical means of concealing its path. In such an instance, the blackskate can make a Survival check (DC 10 + caster level of spell or effect) in order to continue tracking its prey.

Skills: When it is lying still along the seafloor, a blackskate gains a +4 racial bonus on Hide checks.

A blackskate has a +8 racial bonus to any Swim check to perform some special action or avoid a hazard. It can always choose to rake 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 blackskate prefers to lie in wait, concealing itself beneath a thin layer of sand and silt much like a living stingray, and uses its deadly tail attack on the first creature that comes near it. It usually chooses to enter its blood rage at the first opportunity.

A blackskate is made up of cast-off bits of flesh, bone, scale, and cartilage that settle to the ocean floor. Somehow this organic detritus mixes with the dark currents of the blackwater trenches and a terrible undead creature is created. A blackskate's body is difficult to damage: the best way to destroy one is to hack it to pieces, which isn't an easy task in the water.

A blackskate seeks out living, warm-blooded creatures. Though it does not consume blood the way vampires and their ilk do, warm blood drives a blackskate into what merfolk call the blood rage - a state in which the creature becomes even more formidable.

A blackskate is capable of inexorably tracking anyone whose blood it has scented, so long as it and its prey are in the same ocean.

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.