Ghostmaster's minions were two servants indentured to Ghostmaster. They do simple tasks such as fetching files and tomes.
At the height of Ghostmaster's frustration with the Ghostbusters, he noticed only two of his servants were present in Netherworld. As they fetched the Book of Annoying Beings, they revealed the other servants were captured by the Ghostbusters. The Ghostmaster wasn't pleased and sent his three best bounty hunters: Animax, Mist Crawler, and Dark.