Catacombs Red Box is an expansion for Catacombs 3E that allows the game to be played in a fully co-op fashion. This includes support for solo play. The expansion also adds new heroes, monsters, Catacomb Lords, and items for Catacombs 3E. It also adds new content for Catacombs & Castles 2E. The set includes custom dice and a new obstacle for use in either game: the "Trilithon".