Given the pub's name, it seems like the perfect place for warlocks. As they are considered as pariahs in the kingdom, they must operate in the shadows of polite society, and practice their darkarts within hidden enclaves, so that they can escape the prejudice of the public. Thus, the pub's basement and catacombs serve as host to the city's warlock community and act as a training ground for new recruits. They also do not hesitate to assassinate those who would try to reveal their hiding place and activities.
Rather eerily, below the warlock trainer's area there is another area of the Stormwind catacombs, with some empty, open coffins across the floor.