Non-Playable Characters (NPCs) are a subtype of virtual agents that populate video games by endorsing social roles in the narrative. To infer NPCs' roles, players evaluate NPCs' appearance and behaviors, usually by ascribing human traits to NPCs, such as intelligence, likability and morality. In particular, hostile NPCs in video games are essential to build the games' inherent challenges. The three experiments reported here investigated the extent to which the perception of hostility in a military shooter game (including both threat of appearance and aggressiveness in behaviors) is influenced by the appearance and the behaviors of NPCs thanks to perceived intelligence, likability and morality-related questionnaires. Our results first show that hostility is efficiently conveyed through NPCs' behaviors, but not significantly by their appearance. Second, our study allows identifying the main predictors of hostility perception, namely unfriendliness, knowledge and harmfulness.