Maybe could get renamed to Gargoyle Fort, because it isn't much of a big castle...but anyways - a small battle arena where stage knock-outs can happen quickly, while at the same time providing a layout where strategy practice and lobbing your Gachaboms at the best timing possible will be required to best the Staff Ghosts in the Prison Break mode.
The name and idea of the stage are based off Killer Instinct 2, specifically Gargos's stage...hence not only it is named Gargoyle Castle, but also uses that game's stage music as well.