Hammerfish (CR 13)

Gargantuan Magical Beast (Psionic and Aquatic)
Alignment: Usually Neutral
Initiative: +6 (+2 Dex, +4 Improved Initiative); Senses: blindsight and Listen +19

AC: 26 (-4 size, +2 Dex, +18 natural), touch 8, flat-footed 24
Hit Dice: 24d10+144 (276 hp)
Fort +20, Ref +16, Will +9
Speed: Swim 60 ft. (70 ft. with Speed of Thought)
Space: 60 ft./15 ft.
Base Attack +24; Grapple +32
Attack: Bite +34 melee
Full Attack: Bite +34 melee
Damage: Bite 2d8+19
Special Attacks/Actions: Psionics, ram
Abilities: Str 36, Dex 15, Con 22, Int 13, Wis 13, Cha 8
Special Qualities:
Feats: Improved Initiative; Psionic Charge; Speed of Thought; Weapon Focus (bite)
Skills: Listen +19, Move Silently +18, and Swim +21
Advancement: 25-32 HD (Gargantuan), 33-48 HD (Colossal)
Climate/Terrain: Any aquatic
Organization: Solitary or pair
Treasure/Possessions: None

Source: Web

Psionics (Sp): 3/day -- energy barrier, mass concussion, and true concussion. Effective manifester level 14th.

Attack/Defense Modes (Sp): At will -- ego whip, id insinuation/thought shield, mental barrier.

Ram (Sp): This ability is what gave the hammerfish its name. It performs a charge attack to strike the target with its head. One can tell it is getting ready to charge, since the bony plates on its head begin to glow with psionic energy. The physical ram attack causes 4d8+13 points of damage. The energy discharged on contact causes 9d4+9 points of psionic energy damage, with a Fortitude save for half (DC 28). The hammerfish can ram up to three times a day. After it makes all three ram attacks, it can no longer use Speed of Thought or Psionic Charge.

Blindsight (Ex): By sensing vibrations and sounds in the water, the hammerfish has blindsight to an effective range of 10 feet per Hit Die.

Hammerfish engage in combat when they want to eat something, which is generally most of the time they are awake. Their favorite tactic is to ram larger prey and use psionics on the smaller stuff.

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.