Sea Drake (CR 15)

Gargantuan Dragon (Aquatic)
Alignment: Usually neutral
Initiative: +4; Senses: Listen +18 and Spot +18

AC: 26 (-4 size, +20 natural), touch 6, flat-footed 26
Hit Dice: 12d12+60 (138 hp)
Fort +15, Ref +10, Will +11
Speed: 15 ft., swim 60 ft.
Space: 20 ft./15 ft.
Base Attack +12; Grapple +36
Attack: Bite +20 melee, or tail smash +20 melee
Full Attack: Bite +20 melee, or bite +20 melee and 2 tail smashes +15 melee, or 2 tail smashes +20 melee
Damage: Bite 2d8+12, tail smash 1d8+6
Special Attacks/Actions: Constrict ship, crushing blow, swallow whole
Abilities: Str 35, Dex 10, Con 21, Int 11, Wis 12, Cha 18
Special Qualities: Dragon traits, ink cloud, regeneration 2
Feats: Alertness; Great Fortitude; Improved Initiative; Iron Will; Lightning Reflexes
Skills: Appraise +15, Knowledge (local) +15, Knowledge (nature) +15, Listen +18, Spot +18, and Swim +35
Advancement: 13-36 HD (Gargantuan)
Climate/Terrain: Any aquatic
Organization: Solitary
Treasure/Possessions: Double standard

Source: Fiend Folio

Constrict Ship (Ex): Instead of crushing a ship with its tail, a sea drake can wrap its serpentine body around all but the largest ships and crush them or drag them below the waves automatically. This can be done to a rowboat (1 round), keelboats (3 rounds), longships (5 rounds), and sailing ships (10 rounds). Warships and galleys are too large for a sea drake to affect in this way

Crushing Blow (Ex): A sea drake can use its tail flukes to smash a boat to splinters. The ship is hit automatically once every 10 rounds, taking tail smash damage (between attacks the sea drake is submerged). The ship's pilot must make a Reflex saving throw (DC 20) after each hit to keep the vessel from being breached and sinking in 1d10 minutes. Apply a modifier to the DC based on the type of ship: rowboat +4, keelboat +2, sailing ship or longship +0, warship -3, galley -5. Regardless of the ship's saving throw result, characters aboard the ship must make Reflex saving throws (DC 20); a successful save means the character takes 1d4 points of damage; on a failed save, a character on deck is hurled overboard and a character belowdecks takes 2d4 points of damage.

Swallow Whole (Ex): A sea drake can swallow whole any creature at least one size category smaller than itself that it successfully attacks with its bite while in the water. First the sea drake must hold the creature in its mouth with a successful grapple check (grapple bonus +36). A second successful grapple check on the following round means the creature is swallowed whole. Once inside the sea drake, the creature must make Swim checks (DC 15) every round as if in was in turbulent water. Success means in takes 1d3 points of subdual damage but can attack the sea drake's insides; failure means in takes 1d6 points of subdual damage and in must make another Swim check immediately no avoid drowning. (The creature cannot attack when avoiding drowning.) A successful grapple check allows the swallowed creature to climb out of the stomach and return no the sea drake's maw, where another successful grapple check is needed to get free. Alternatively, a swallowed creature can try to cut its way out with either claws or a light piercing or slashing weapon. Dealing a total of at least 35 points of damage to the stomach (AC 20) in this way causes the sea drake to disgorge the entire contents of its stomach. A sea drake's stomach can hold 2 Large, 4 Medium-size, or 16 Small or smaller opponents.

Dragon Traits: Sea drakes are immune to sleep and paralysis effects. They have darkvision (60-foot range) and low-light vision.

Ink Cloud (Ex): If the sea drake feels it needs to escape, it can cloud the water around it with ink. This acts just like a darkness spell under water with a 50-foot radius and a duration of 5 minutes.

Regeneration (Ex): A sea drake takes normal damage while out of water. Attack forms that don't deal hit point damage ignore regeneration, and the sea drake does not restore hit points lost from starvation, thirst, or suffocation. If a sea drake loses a limb or body part, the lost portion regrows in 3d6 minutes. The creature can reattach the severed member instantly by holding it to the stump. Severed parts that are not reattached wither and die normally.

Skills: Sea drakes have a +8 racial bonus on any Swim check to perform some special action or avoid a hazard and can always choose to take 10 on Swim checks, even if distracted or endangered.

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.