Lurker (CR 3)

Large Aberration
Alignment: Always neutral
Initiative: +1 (Dex); Senses: darkvision 60 ft., Listen +2, and Spot +2

AC: 15 (-1 size, +1 Dex, +5 natural), touch 10, flat-footed 14
Hit Dice: 6d8+18 (45 hp)
Fort +5, Ref +3, Will +5
Speed: 10 ft., fly 30 ft. (average)
Space: 10 ft./5 ft.
Base Attack +4; Grapple +12
Attack: Slam +8 melee (1d8+6)
Full Attack: Slam +8 melee (1d8+6)
Damage: -
Special Attacks/Actions: Constrict 1d6+6, improved grab
Abilities: Str 19, Dex 13, Con 16, Int 2, Wis 11, Cha 12
Special Qualities: -
Feats: Alertness; Stealthy; Weapon Focus (slam)
Skills: Hide +6, Listen +2, Move Silently +5, and Spot +2
Advancement: 7-12 HD (Large); 13-18 HD (Huge)
Climate/Terrain: Underground
Organization: Solitary
Treasure/Possessions: 1/10 coins; 50% goods; 50% items

Source: Underdark

Constrict (Ex): A lurker deals 1d6+6 points of damage with a successful grapple check.

Improved Grab (Ex): If a lurker hits a Medium or smaller opponent with its slam attack, it deals normal damage and attempts to start a grapple as a free action without provoking an attack of opportunity (grapple bonus +12). If it gets a hold, it wraps itself around the victim and constricts.

Any attacks that hit a lurker while it is wrapped around a foe deal half their damage to the monster and half to the trapped victim.

Skills: A lurker receives a +12 racial bonus on Hide checks in natural rocky areas.

A lurker drops from the ceiling onto potential prey and endeavors to wrap around it and crush it.