You let your foe's friends know that proximity to the foe adds an element of danger.

Encounter   ✦     Martial, Weapon
Standard Action      Ranged weapon

Target: One creature

Attack: Dexterity vs. AC

Hit: 3[W] + Dexterity modifier damage. When an enemy moves into a square within 2 squares of the target before the start of your next turn, you can make a ranged basic attack with a weapon against that enemy as a free action.

Published in Dragon Magazine 383, page(s) 51.