The phrase denotes attire themed around the popular mobile strategy game, Clash of Clans, specifically designed for the Halloween season. These outfits often replicate in-game characters like Barbarians, Archers, Wizards, and Giants. For example, a child might dress as a Barbarian King, complete with a horned helmet and a massive foam sword.
The appeal lies in combining the widespread enthusiasm for the game with the festive spirit of Halloween. This allows fans to express their affinity for Clash of Clans in a tangible way, participating in costume parties and trick-or-treating while showcasing their favorite characters. Historically, character-based ensembles have always been a mainstay of Halloween, and this category simply extends that tradition to the digital realm.