Players of digital games are limited by the constraints of the game's implementation. Players cannot fly a kite, plant a tree or make friends with a dragon if these activities were not coded within the game. Game orchestration relaxes these restrictions by allowing players to create game narratives and settings as the game is being played. This enables players to express their creativity beyond the strictures of the game's implementation. We present Tabula Rasa, a novel game orchestration tool based on an efficient tabletop interface. Based on a study of 20 game orchestration sessions using Tabula Rasa, we identify five behavioural patterns adopted by orchestrators, and four styles of collaborative interaction between orchestrators and players. Finally, we present recommendations for designers of game orchestration systems.