Shadowy Mercenary

Shadowy Mercenaries are human ghosts found in Sword's Rest of the Halls of Reflection.

These are likely supposed to represent the mercenaries that Arthas hired to burn his ships in the "Dissension" mission of Warcraft III. He then betrayed these mercenaries and had his men kill them. However, the mercenaries in Warcraft III were composed of ice trolls and an ogre, with no humans in their ranks, and Arthas referred to them as "creatures". Similarly, in the quest The Forgotten Tale, the ghosts on the Forgotten Shore refer to the mercenaries as "savage beasts".

On the other hand, the Death Knight manga shows human mercenaries. Since the manga and patch 3.3 were released around the same time, around a year after the release of Wrath of the Lich King and the addition of The Forgotten Tale, this may be an intentional retcon.

In Warcraft III: Reforged, Arthas' mercenaries are again called "creatures" and depicted as trolls and an ogre, indicating the original story still stands.