rare cg gargantuan amphibious dragon water 

Perception +30; darkvision, wavesense (imprecise) 60 feet

Languages Aquan, Auran, Celestial, Common, Draconic, Elven

Skills Acrobatics +32, Arcana +26, Athletics +33, Deception +25, Intimidation +27, Nature +28, Society +26, Stealth +32, Survival +26

Str +8 Dex +7 Con +5 Int +3 Wis +5 Cha +4

AC  41; fed by metal; Fort +29, Ref +32, Will +27

HP 350; Immunities paralyzed, sleep

Frightful Presence (aura, emotion, fear, mental) 90 feet, DC 36 (page 305)

Vortex (aura, water) 40 feet. Water in the aura that's also in the same body of water as the dragon is difficult terrain for Swimming creatures which don't have the water trait.

Liquefy [R] (abjuration, arcane, water) Trigger The dragon is targeted by a Strike or spell that could deal fire or physical damage to them; Effect The dragon liquefies, turning entirely to water while maintaining their shape, for a split second. Against the triggering effect, they gain resistance 25 to fire and to all physical damage.

Speed 50 feet, fly 140 feet, swim 70 feet; water walk

Melee [>] jaws +34 (magical, reach 20 feet), Damage 3d12+16 piercing plus hyponatremia

Melee [>] claw +34 (agile, magical, reach 15 feet), Damage 3d10+16 slashing plus Grab

Melee [>] tail +34 (magical, reach 25 feet), Damage 3d10+16 bludgeoning plus Grab

Arcane Innate Spells DC 38; 5th control water, create water (at will); 3rd endure elements (self only); Constant (2nd) water walk

Breath Weapon [>>] (arcane, evocation, water) The dragon shoots a ball of water that deals 18d6 bludgeoning damage in a 30-foot burst within 60 feet (DC 38 basic Reflex save). All non-magical fire in the radius is extinguished. The dragon can't use Breath Weapon again for 1d4 rounds.

Coiling Frenzy [>>] The dragon makes one claw Strike and one tail Strike in either order, each against the same target. If either Strike hits, the dragon automatically Grabs the target.

Draconic Momentum The dragon recharges their Breath Weapon whenever they score a critical hit with a Strike.

Greater Constrict [>] 3d10+8 bludgeoning, DC 38 (page 305)

Hyponatremia (water) A living creature that takes damage from the sea dragon's jaws Strike must succeed at a DC 38 Fortitude save or become sickened 2 as a surge of excess water floods its body.

Tidal Wave [>>>] (arcane, evocation, manipulate, water) Frequency once per 10 minutes; Requirements The dragon is in a body of water at least as large as they are; Effect The dragon slams their body down, sending a towering wave outward. This wave deals 10d12 bludgeoning damage in a 90-foot emanation. Each creature in the area must attempt a DC 38 Reflex save. Structures and unattended objects in the area take the full amount of damage with no saving throw. Critical Success The creature takes no damage but is pushed 30 feet from the dragon.Success The creature takes half damage and is pushed 60 feet from the dragon.Failure The creature takes full damage, is pushed 120 feet from the dragon, and falls prone.Critical Failure As failure, but double damage.

Bestiary 3, page 78.