Kapoacinth (CR 4)

Medium Magical Beast (Aquatic)
Alignment: Usually chaotic evil
Initiative: +2 (Dex); Senses: darkvision 60 ft., Listen +4, and Spot +4

AC: 16 (+2 Dex, +4 natural), touch 12, flat-footed 14
Hit Dice: 4d8+19 (37 hp); DR: 10/magic
Fort +5, Ref +6, Will +4
Speed: 40 ft., swim 60 ft. (average)
Space: 5 ft./5 ft.
Base Attack +4; Grapple +6
Attack: Claw +6 melee
Full Attack: 2 claws +6 melee and bite +4 melee and gore +4 melee
Damage: Claw 1d4+2, bite 1d6+1, gore 1d6+1
Special Attacks/Actions: -
Abilities: Str 15, Dex 14, Con 18, Int 6, Wis 11, Cha 7
Special Qualities: freeze
Feats: Multiattack; Toughness
Skills: Hide +7*, Listen +4, and Spot +4
Advancement: 5-6 HD (Medium-size); 7-12 HD (Large)
Climate/Terrain: Any aquatic and underground
Organization: Solitary, pair or wing (5-16)
Treasure/Possessions: Standard

Source: Monster Manual

Freeze (Ex): A kapoacinth can hold itself so still it appears to be a statue. An observer must succeed at a Spot check (DC 20) to notice the kapoacinth is really alive.

Skills: Kapoacinths receive a +8 racial bonus to Hide checks when concealed against a background of worked stone.

Kapoacinths either remain still, then suddenly attack, or dive onto their prey, using their wings to fly through the water.

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.