This massive horror looks like a shark protected by a crab carapace, with a tail, flanks, and pectoral fins covered in cruel hooks.
Isonade CR 15
CE Gargantuan magical beast (aquatic)
Init +1; Senses darkvision 120 ft., Keen Scent; Perception +28
AC 28, touch 8, flat-footed 26 (+1 Dex, +1 dodge, +20 natural, -4 size)
hp 230 (20d10+120)
Fort +18, Ref +13, Will +13
Speed swim 100 ft.
Melee bite +29 (2d8+12 plus grab), 2 fins +28 (2d8+12 plus grab), tail slap +23 (2d8+6 plus grab)
Space 20 ft.; Reach 20 ft. (30 ft. with tail slap)
Special Attacks capsize, fast swallow, hooked appendages, swallow whole (3d6 bludgeoning damage, AC 20, 23 hp)
Str 34, Dex 13, Con 22, Int 13, Wis 20, Cha 9
Base Atk +20; CMB +36 (+40 drag, grapple); CMD 48 (50 vs. drag)
Skills Perception +28, Stealth +18 (+28 in deep water), Swim +43; Racial Modifiers +10 Stealth in deep water
Languages Aquan, Common
Environment any oceans
Hooked Appendages (Ex) An isonade gains a +4 circumstance bonus on combat maneuver checks to grapple. When using the Spring Attack feat, an isonade can attempt a grapple or drag combat maneuver in place of its melee attack.
The dreaded isonade is a silent killer. Many a sailor has spotted a dark shape in the waters below, only to turn around in time to see his mate being dragged overboard, impaled on a spiny tail. A ship's captain who plans to sail through an isonade's waters often takes on extra crew, knowing that at least a few crew members might simply disappear over the side before they reach port. Though few alive have ever seen the monster's full body, a great many sailors have caught a glimpse of its hooked carapace as it drags a skewered sailor down to the inky depths.
Mercifully, isonades spend much of their existence in hibernation. When an isonade is preparing to hibernate, the population in its area of the ocean drops drastically while the beast consumes huge quantities of food. Though an isonade will eat just about anything that bleeds, it favors massive beasts to minimize time spent hunting—such as giant squid or whales—though it will resort to eating hundreds of fish once larger prey grow scarce. It's also intelligent enough to know that a seafaring vessel contains a large quantity of warm and screaming snacks all isolated in one convenient place. An isonade can hibernate for hundreds of years, waking only when its vast store of food has been exhausted or when startled by a natural disaster, such as an earthquake or volcanic eruption.
Because of this long hibernation, rumors of isonades are often exaggerated and relegated to myth, making their exact territories hard to predict when they awaken once again. The isonade's eating cycle provides indicators of its return. An abundance of fish in a region can signal a hungry isonade's territory, as sudden explosions in the fish population sometimes occur when these beasts begin devouring the region's larger predators. An isonade shakes off its torpor by eating the large, slow animals in the depths, but inevitably circles upward as its appetite grows.
An isonade can live for over 10,000 years, and can grow to over 70 feet in length. An adult isonade weighs approximately 300,000 pounds.