Halycon's Muzzle

 is a rare Leather armor Shoulder piece that is received as a quest reward.

Source
This item is a reward from the Horde quest which starts with Warlord Goretooth in Kargath within the Badlands. To complete the quest, you must complete the following:

Retrieve:
 * 1 Important Blackrock Documents

Kill:
 * 1 x Highlord Omokk
 * 1 x War Master Voone
 * 1 x Overlord Wyrmthalak