You enchant your ammunition with poisoning magic, then transfer that enchantment onto one of your allies close to the target.

Encounter   ✦     Arcane, Poison, Weapon
Standard Action      Ranged weapon

Target: One creature

Attack: Intelligence vs. AC

Hit: 2[W] + Intelligence modifier poison damage, and choose one ally within 5 squares of the target. Until the end of your next turn, any creature that hits that ally with a melee attack takes poison damage equal to your Wisdom modifier.

Revision (11/30/2009)
Page 19: Halo of Thorns: add the Weapon keyword and make it a standard action.

Published in Dragon Magazine 381, page(s) 56.