Here's an archery-themed NPC for your players to contend with. The backstory is specific to Eberron but it shouldn't be to hard to fit her into any fantasy campaign where specialized magic items are available.
One of the most formidable agents of the Shadow Network is Aenyssa d'Thuranni. Aenyssa survived the Shadow Schism by staying out of the way and conducting "eliminations" of targets not related to either the Phiarlans or the Paelions. There are rumors that Aenyssa was romantically involved with the youngest son of Lord Tolar Paelion d’Phiarlan, head of the extinct Paelion line of House Phiarlan, but she flatly denies them. A skilled acrobat and professional killer, Aenyssa is credited (privately, of course) with dozens of murders; her most notable was the assassination of Cardinal Jostek of the Church of the Silver Flame, in which she shot her victim through an arrow slit in one of the Church's great cathedrals from the opposite side of the keep.
Aenyssa has a pair of immovable shafts (see Adventurer's Vault page 173) that she uses as part of her trade. As a trained acrobat, she can use the immovable shafts to scale walls and ascend vertical shafts with ease. Her crossbow has a recess in the stock that she can use to mount one immovable shaft. When Aenyssa activates the shaft, it locks the crossbow in place to form the perfect stabilizer. She is comfortable spending hours suspended from the immovable shafts and can use them to support her weight; combined with her Mark of Shadow, she can strike from almost anywhere.
4th Edition D&D statistics
Medium fey humanoid, elf
Level 10 Lurker; XP 500
Senses Perception +14, darkvision
HP 160; Bloodied 80
AC 24; Fortitude 20; Reflex 23; Will 21
(m) Dagger (standard; at-will) • Weapon
+13 vs. Reflex; 1d4 + 7 damage.
(r) Crossbow (standard; at-will) • Weapon
Ranged 15/30; +15 vs. AC; 1d8 + 5 damage.
(R) Shadowblind (Standard; recharge 5,6)
Ranged 10; +11 vs. Will: 2d6 + 5 damage, and the target is blinded (save ends).
(R) Stabilized Shot (Standard; encounter)
Special: Aenyssa must spend at least 1 round taking no actions in preparation. During this period, Aenyssa's speed is 0 and she cannot be pushed, pulled, or slid.
Ranged 30; +15 vs. Reflex; 3d8 damage on a hit; half damage on a miss. If the target is granting combat advantage, the damage is maximized.
Cloak of Shadows (Standard; at-will)
Aenyssa gains total concealment from all creatures until she hits with an attack.
Aenyssa deals 2d8 extra damage on attacks against any creature granting combat advantage to her.
Mark of Shadow
When Aenyssa misses with an attack while hidden, she remains hidden.
Elven Accuracy (free; encounter)
Aenyssa can reroll an attack roll and must use the second roll.
Aenyssa ignores difficult terrain when she shifts.
Languages Common, Elven
Skills Acrobatics +16, Bluff +13, Stealth +16, Thievery, +16
Str 16 (+8) Dex 22 (+11) Wis 18 (+9)
Con 12 (+6) Int 12 (+6) Cha 16 (+8)
Equipment leather armor, 1 daggers, crossbow with 20 bolts, 2 immovable shafts