Kopru (CR 6)

Medium Monstrous Humanoid (Aquatic)
Alignment: Always chaotic evil
Initiative: +2 (Dex); Senses: darkvision 60 ft.

AC: 15 (+2 Dex, +3 natural), touch 12, flat-footed 13
Hit Dice: 8d8 (36 hp)
Fort +2, Ref +8, Will +9
Speed: 5 ft., swim 40 ft.
Space: 5 ft./5 ft.
Base Attack +8; Grapple +10
Attack: Tail slap +10 melee and 2 claws +8 melee and bite +8 melee
Full Attack: Tail slap +10 melee and 2 claws +8 melee and bite +8 melee
Damage: Tail slap 1d6+2, claw 1d4+1, bite 1d4+1
Special Attacks/Actions: Constrict 3d6+3, dominate person, improved grab
Abilities: Str 15, Dex 14, Con 11, Int 11, Wis 12, Cha 10
Special Qualities:
Feats: Iron Will; Multiattack; Skill Focus (Escape Artist)
Skills: Concentration +8, Escape Artist +11, Move Silently +6, Search +4, and Swim +10
Advancement: 9-10 HD (Medium-size); 11-12 HD (Large)
Climate/Terrain: Warm aquatic and marsh
Organization: Solitary, pair, patrol (3-5), or colony (6-24)
Treasure/Possessions: Standard coins (gold and platinum only), standard goods (gems only), no items

Source: Monster Manual II

Constrict (Ex): With a successful grapple check, a kopru can constrict a grabbed opponent, dealing 3d6+3 points of bludgeoning damage.

Dominate Person (Su): Once per day, a kopru can produce an effect like that of a dominate person spell (caster 10th; Will save DC 14), except that the range is 180 feet and the duration is eight days.

Improved Grab (Ex): If a kopru hits an opponent that is its own size or smaller with a tail attack, it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity (grapple bonus +17, including a +7 racial bonus on grapple checks). If it gets a hold, it also constricts in the same round. Thereafter, the kopru has the option to conduct the grapple normally, or simply use its tail to hold the opponent (-20 penalty on grapple check, but the kopru is not considered grappled). In either case, each successful grapple check it makes during successive rounds automatically deals tail and constrict damage.

Out of the water, a kopru is nearly helpless. On land, it cannot attack with its claws because it needs its arms to drag itself across the ground or prop its body up. A kopru in water, however, is a ferocious opponent in melee combat. Along with its claws and teeth, it lashes out with its tails, all three of which strike as one.

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.