Assassin Vine (CR 3)

Large Plant
Alignment: Always neutral
Initiative: +0; Senses: blindsight 30 ft. and low-light vision

AC: 15 (-1 size, +6 natural), touch 9, flat-footed 15
Hit Dice: 4d8+12 (30 hp)
Fort +7, Ref +1, Will +2
Speed: 5 ft.
Space: 10 ft./10 ft. (20 ft. with vine)
Base Attack +3; Grapple +12
Attack: Slam +7 melee
Full Attack: Slam +7 melee
Damage: Slam 1d6+7
Special Attacks/Actions: constrict 1d6+7, Entangle, improved grab
Abilities: Str 20, Dex 10, Con 16, Int -, Wis 13, Cha 9
Special Qualities: Camouflage, immunity to electricity, plant traits, resistance to cold 10 and fire 10
Advancement: 5-16 HD (Huge); 17-32 HD (Gargantuan); 33+ HD (Colossal)
Climate/Terrain: Temperate forest
Organization: Solitary or patch (2-4)
Treasure/Possessions: 1/10th coins; 50% goods, 50% items

Source: Monster Manual

Entangle (Su): An assassin vine can animate plants within 30 feet of itself as a free action. The effect lasts until the vine dies or decides to end it (also a free action). The ability is otherwise similar to entangle as cast by a 4th-level druid (save DC 13).

Improved Grab (Ex): To use this ability, the assassin vine must hit with its slam attack.

Constrict (Ex): An assassin vine deals 1d6+7 points of damage with a successful grapple check against Medium-size or smaller creatures.

Blindsight (Ex): Assassin vines have no visual organs but can ascertain all foes within 30 feet using sound, scent, and vibration.

Camouflage (Ex): Since an assassin vine looks like a normal plant when at rest, it takes a successful Spot check (DC 20) to notice it before it attacks. Anyone with Survival, or Knowledge (plants or herbs) can use those skills instead of Spot to notice the plant. Dwarves can use stonecunning to notice the subterranean version.

Assassin vines use simple tactics: They lie still until prey comes within reach, then attack. They use their entangle ability both to catch prey and to deter counterattacks.