Wyste (CR 5)

Huge Aberration
Alignment: Always neutral
Initiative: +1 (Dex); Senses: blindsense, Listen +6, and Spot +6

AC: 18 (-2 size, +1 Dex, +9 natural), touch 9, flat-footed 17
Hit Dice: 5d8+25 (47 hp)
Fort +6, Ref +2, Will +4
Speed: 10 ft., swim 40 ft.
Space: 15 ft./10 ft.
Base Attack +3; Grapple +7
Attack: 7 tentacle rakes +5 melee
Full Attack: 7 tentacle rakes +5 melee
Damage: Tentacle rake 1d4+6
Special Attacks/Actions: Improved grab, bite
Abilities: Str 22, Dex 13, Con 20, Int 1, Wis 11, Cha 8
Special Qualities: acid immunity
Feats: Alertness; Improved Critical (bite)
Skills: Listen +6, Spot +6, and Swim +14
Advancement: 6-15 HD (Huge)
Climate/Terrain: Any underground
Organization: Solitary, pair or school (3-8)
Treasure/Possessions: None

Source: Monster Manual II

Bite (Ex): when a wyste grapples an opponent, its tentacles draw the victim to its toothed sucker hole. On the round after the wyste grabs, it makes a regular attack with its bite (in lieu of any claw attacks), gaining a +4 bonus on the attack roll (+11 melee). If the bite attack misses, the wyste drops the character, who falls prone in front of the creature. If the bite attack is successful, the victim takes 1d6+9 points of damage. The wyste can then deal bite damage automatically every round. The victim can escape by winning an opposed grapple check against the wyste, making a successful Escape Artist check against the wyste's grapple check result, or by killing the wyste.

Improved Grab (Ex): If a wyste hits a Large or smaller opponent with one or more tentacle attacks, it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity (grapple bonus +17, plus a +2 bonus for each tentacle that hit beyond the first). The wyste can make only one grapple attack per round, no matter how many tentacles it devotes to the effort. If it gets a hold, it has the option to conduct the grapple normally, or simply use its tentacles to hold the opponent (-20 penalty on grapple check, but the wyste is not considered grappled). In either case, each successful grapple check it makes during successive rounds automatically deals damage for all the tentacles used to hold the opponent.

Blindsight (Ex): A wyste is blind, but its tentacles are sensory organs that can ascertain prey by scent and vibration. This ability enables it to discern objects and creatures within 120 feet. A wyste usually does not need to make Spot or Listen checks to notice creatures within range of its blindsight.

A wyste lunges up to 15 feet out of its slimy pools to attack creatures that approach. wystes in an area often attack as a group; others nearby might be attracted by the commotion, too. when a wyste kills a victim, it drags its prey away to be consumed at leisure.