Marine Saurian Working Draft
Marine Saurian
Gargantuan Animal
Hit Dice: 14d8+84 (147 hp)
Initiative: +1
Speed: Swim 40 ft.
Armor Class: 18 (-4 size, +1 Dex, +11 natural), touch 7, flat-footed 17
Base Attack/Grapple: +10/+34
Attack: Bite +19 melee (3d8+18/19-20) or tail slap +18 melee (3d6+18)
Full Attack: Bite +19 melee (3d8+18/19-20) or tail slap +18 melee (3d6+18)
Space/Reach: 20 ft./15 ft.
Special Attacks: Death roll, improved grab, tail sweep, swallow whole
Special Qualities: Hold breath, low-light vision
Saves: Fort +15, Ref +10, Will +4
Abilities: Str 35, Dex 12, Con 23, Int 1, Wis 12, Cha 2
Skills: Hide +2*, Listen +6, Spot +6, Swim +16
Feats: Alertness, Endurance, Improved Critical (bite), Skill Focus (Hide), Weapon Focus (bite)
Environment: Warm aquatic
Organization: Solitary or pair
Challenge Rating: 9
Treasure: None
Alignment: Always neutral
Advancement: 15-30 HD (Gargantuan), 31-56 HD (Colossal)
Level Adjustment: —
A smooth-skinned reptile as big as a whale, with a sinuous body and long tail shaped for swimming. Its four limbs are so flattened for steering through water they are useless for walking.
Marine saurians are immense aquatic reptiles. They come in several varieties, leading some sages to speculate they include multiple species of reptile of similar size and habits, possibly including giant mosasaurs, pliosaurs, and crocodiles. All marine saurians resemble immense crocodiles in rough shape, with flippers or web-footed legs for limbs. Some have a vertical fin on the end of the tail, while others have flattened scull-like tails. They are mostly smooth-skinned and streamlined, but may have traces of scales forming a ridge down their back and/or rings around their body. Marine saurians live in tropical waters and avoid coasts.
Marine saurians are surprisingly shy. They eat smaller sea creatures (mostly large fish and small whales), but tend to avoid or hide from anything they don't recognize as prey or a potential mate.
A marine saurian is usually about 60 feet long and weighs roughly 50 tons.
Combat
Despite having a retiring personality, marine saurians are deadly predators able to tear a whale to pieces. They generally target their largest opponent with bite attacks and follow up with a death roll once they secure a grapple. Marine saurians usually only use tail slaps when their jaws are occupied by prey and they need to attack a second opponent. Multiple lesser enemies are often dealt with by tail sweep attacks.
Death Roll (Ex): A marine saurian can perform a death roll as a standard action by making a successful grapple check. It tucks in its legs and rolls rapidly, twisting and wrenching the opponent in its jaws. The opponent takes twice the marine saurian's bite damage and must succeed at a DC 29 Fortitude save or be knocked prone and stunned for 1d3 rounds. If successful, the saurian maintains its grapple.The save DC is Strength-based.
Hold Breath (Ex): A marine saurian can hold its breath for a number of rounds equal to 10 × its Constitution score before it risks drowning.
Improved Grab (Ex): To use this ability, a marine saurian must hit with its bite attack. It can then attempt to start a grapple as a free action without provoking an attack of opportunity. If it wins the grapple check, the saurian establishes a hold on the opponent with its mouth and drags it into deep water, attempting to pin it to the bottom or swallow the foe.
Swallow Whole (Ex): A marine saurian can try to swallow a grabbed opponent up to two size categories smaller than itself by making a successful grapple check. Once inside, the opponent takes 2d8+12 points of crushing damage plus 8 points of acid damage per round from the saurian’s gizzard. A swallowed creature can cut its way out by using a light slashing or piercing weapon to deal 25 points of damage to the gizzard (AC 15). Once the creature exits, muscular action closes the hole; another swallowed opponent must cut its own way out. A Gargantuan saurian’s interior can hold 2 Large, 8 Medium, 32 Small, 128 Tiny, or 512 Diminutive or smaller opponents.
Tail Sweep (Ex): A marine saurian can sweep its tail as a standard action, affecting a half-circle with a radius equal to its Reach. All creatures within the swept area that are three or more size categories smaller than the marine saurian automatically take damage equal to the saurian's tail-slap attack. Affected creatures can attempt DC 29 Reflex saves to take half damage. The save DC is Strength-based.
Skills: A marine saurian 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.
*A marine saurian gains a +4 racial bonus on Hide checks when in the water. Further, a marine saurian can lie in the water with only its eyes and nostrils showing, gaining a +10 cover bonus on Hide checks.
Originally appeared in Dragon Magazine #190 (1993).
But I'm fine with your suggestion. Any ideas on background and description? You're the cryptozoologist. 
