Gnoll Decoys are a Darkmoon Faire product, like those used in Whack-a-Gnoll. Purchased by Captain Ripflesh, he uses them when adventurers seek  Justice. Ripflesh drops their [Crumpled Bill of Sale]:
Crumpled Bill of Sale
Darkmoon Faire Bill of Sale
6x Super-effective Gnoll Decoy*
60G 20S 300C
* Effectiveness of Super-effective Gnoll Decoy may depend on intelligence of opponent. Not warranted for use against Humanoids, Dragonkin, or other semi-sentient creatures.