Threatening Reach

A creature that has threatening reach can make an opportunity attack against any enemy within its reach that provokes an opportunity attack.

Published in Monster Manual 2, page(s) 219, Monster Manual, page(s) 283, Player's Handbook 3, page(s) 223, Rules Compendium, page(s) 317, Monster Vault: Threats to the Nentir Vale, page(s) 125.