Thorn (CR 4)

Small Fey
Alignment: Usually neutral
Initiative: +6 (+2 Dex, +4 Improved Initiative); Senses: low-light vision, Listen +9, and Spot +9
Languages: Common and Sylvan

AC: 19 (+1 size, +2 Dex, +3 natural, +2 leaf leather armor, +1 buckler), touch 13, flat-footed 17
Hit Dice: 6d6+12 (33 hp); DR: 5/cold iron
Fort +4, Ref +7, Will +5
Speed: 20 ft.
Space: 5 ft./5 ft.
Base Attack +3; Grapple +2
Attack: Thorn longsword +8 melee or longbow +6 ranged
Full Attack: Thorn longsword +8 melee or longbow +6 ranged
Damage: Thorn longsword 1d6+3/19-20, longbow 1d6/x3
Special Attacks/Actions: Sleep arrows, sneak attack +2d6
Abilities: Str 16, Dex 15, Con 13, Int 10, Wis 10, Cha 13
Special Qualities:
Feats: Improved Initiative; Stealthy; Weapon Focus (longsword)
Skills: Diplomacy +3, Hide +17, Listen +9, Move Silently +13, Search +9, Sense Motive +9, Spot +9, and Survival +0 (+2 following tracks)
Advancement: By character class
Climate/Terrain: Temperate forests
Organization: Solitary, pair, or patrol (3-5)
Treasure/Possessions: Standard

Source: Monster Manual III

Sleep Arrows (Ex): Thorns carry the sleep arrows commonly used by pixies. Any opponent struck by one of these arrows, regardless of Hit Dice, must succeed on a DC 16 Fortitude save or be affected as though by a sleep spell. The save DC is Charisma-based and includes a +2 racial bonus.

Sneak Attack (Ex): A thorn can sneak attack as a rogue, gaining an extra 2d6 points of damage on a successful sneak attack.

Thorns generally do not pick fights, but they will attack anyone or anything that threatens or harms other fey. Like most fey, though, they don't take a direct approach. Instead, they are sneaky creatures that launch vicious attacks from hiding.