AI is increasingly being used to moderate player behaviour in online multiplayer games, working to identify and respond to toxic and problematic conduct with greater efficiency and accuracy than existing automated systems. However, little work has explored the application of AI moderation in the gaming ecosystem, despite growing ethical concerns about AI applications in other domains. In this study, we conducted 2 expert workshops and interviewed 26 players and industry professionals on their understandings, perceptions and experiences with AI moderation in multiplayer games. Applying a metaphorical frame via template analysis, we outline four metaphors that capture participants' views on the roles of AI and automation in moderation: the Unreliable Police Force, the Unscrupulous Governor, the Uncaring Judge, and the Untiring Assistant. We discuss these roles as exacerbating a top-down, punitive online justice system and identify ethical concerns around transparency, fairness and inclusion, privacy, and human-AI collaboration. To address these concerns, we put forward a set of ethical design considerations and alternative roles for AI moderation in multiplayer games.