Blackhowl

The Blackhowl are a group of Gilneans who were manipulated by Creed, a black drakonid in disguise as an affluent Gilnean noble calling himself Lord Hiram Creed. The group was made up of both Gilnean humans and worgen occupying Gilneas City. Creed had infected them with his own draconic blood, which enhanced their physical capabilities but also unwittingly kept them loyal to Creed. The blood also had a possibility of killing the Gilneans as it worked its way out of their system.

The Blackhowl apparently repelled numerous Forsaken assaults, as seen in the courtyard of the Stoneward Prison where Creed resided, which was littered with Forsaken corpses. Black Prince Wrathion sent his rogue champion, who sought to earn his favor, to assassinate Creed in his crusade to eliminate all corrupted black dragons on Azeroth. With his death, it is unknown what the fate of the Blackhowl group is, though it is probable they kept guarding Gilneas City.

Named

 * (leader)

In Hearthstone
The Blackhowl are represented in the The Witchwood expansion for Hearthstone by a legendary warrior card, the. The Blackhowl are a group committed to the defense of Gilneas. Their leader Creed was secretly a corrupted drakonid in disguise (who performed some icky blood rituals) and was "retired". The fate of the remaining Blackhowl were unknown... until now.

Speculation

 * Wrathion and his followers claimed that the Gilneans had no clue of their subversion, so at the time they might've been fighting for the Alliance. However Creed later turned them all into his loyal servants with his draconic blood, and they were also hostile to Alliance rogues sent to kill Creed. Creed also fought the Forsaken within Gilneas. It thus seems that Creed sought to take Gilneas for himself or his flight, turning its inhabitants into his unwilling servants.
 * Zazzo states that following Creed's death, the Blackhowl were "on their own" again. It is thus possible that those that survived and were not turned into Creed's servants might have been re-integrated in the Gilnean forces of the Alliance out in the Ruins of Gilneas. However, it was also stated that Gilneas was abandoned after the events of Cataclysm.
 * In Hearthstone, the Blackhowl did return to the Alliance.