Shadows are some of the Lich King's most frightening creatures. Some of these creatures appeared during the Scourge Invasion. These acolytes could be revealed using the necrotic runes they carried, and then destroyed with magic or strength of arms. When the shadows were destroyed, it was only a matter of time before the Lich King decided to recall his necropolises and leave the defenders in peace.
The Shadow Orb was seen in Warcraft III.