Hammerclaw (CR 4)

Large Magical Beast (Aquatic)
Alignment: Usually neutral evil
Initiative: +4; Senses: darkvision 60 ft., Spot +5, and listen +5
Languages: Aquan (a few words)

AC: 18 (-1 size, +9 natural), touch 9, flat-footed 18
Hit Dice: 6d10+18 (54 hp)
Fort +8, Ref +5, Will +5
Speed: 20 ft., swim 20 ft.
Space: 10 ft./10 ft.
Base Attack +6; Grapple +14
Attack: Claw +9 melee
Full Attack: 2 claws +9 melee
Damage: Claw 1d6+4
Special Attacks/Actions: Constrict 2d6+4, improved grab, sonic pulse
Abilities: Str 19, Dex 10, Con 17, Int 4, Wis 12, Cha 8
Special Qualities: Amphibious, resistance to sonic 10
Feats: Alertness; Improved Initiative; Iron Will
Skills: Hide +5 (+9 in rocky areas), Spot +5, Swim +12, and listen +5
Advancement: 7-12 HD (large); 13-18 HD (Huge)
Climate/Terrain: Temperate aquatic
Organization: Solitary or pair
Treasure/Possessions: Standard

Source: Stormwrack

Constrict (Ex): A hammerclaw deals 2d6+4 points of damage when it wins a grapple check.

Improved Grab (Ex): To use this ability, a hammerclaw must hit an opponent of its own size or smaller with a claw attack. It can then attempt to start a grapple as a free action without provoking attacks of opportunity. If it wins the grapple check, it establishes a hold and can constrict.

Sonic Pulse (Su): A hammerclaw can create a deadly cone of sonic energy by snapping its great claw. This cone has a range of 30 feet. Any creature within the area takes 4d6 points of sonic damage and is stunned for 1d4 rounds. A DC 16 Fortitude save negates the stun and halves the damage. The save DC is Constitution-based.

Amphibious (Ex): Although the hammerclaw is aquatic, it can survive indefinitely on land.

Skills: A hammerclaw's mottled shell gives it a +4 racial bonus on Hide checks, which improves to +8 in areas of coral or rock. A hammerclaw 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.

Hammerclaws wait to begin a combat until their foe wanders within range of their sonic bolt. They seek to quickly stun their prey, then scuttle forward seize and devour the hapless victim before it recovers from its stunned state.

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.