The Pan-Dimensional Liquid Beast from The Mogadon Cluster was an unseen entity which attacked the Boys from the Dwarf one Christmas Day. This during the time that they had lost Red Dwarf and were searching for it aboard Starbug. Dave Lister used that Christmas as an example of how every day was just another slog through Deep Space, until Kryten reminded him about the attack from the beast. (RD: Out of Time, Series VI)