In an approach, one or more player characters controllable by a first player account perform an action in an instance of a game world. In the event that the action meets one or more conditions for creating a nemesis, a computer system controlling the game instance selects a second player account to be invaded by a nemesis. When the second player account plays the game in the same or a different game instance, the computer system determines whether second one or more characters of the selected account meet one or more invasion conditions. If the invasion conditions are met, the computer system generates computer-controlled enemy NPCs for second one or more characters of the second player account to defeat. If the second account defeats the nemesis invasion, rewards are generated for the first and second player accounts. Otherwise, the computer system chooses a third player account for nemesis invasion.