Thanks for the clarification! He could find out that the Sylphid are essentially only looking for compatibility with their procreation methods. There are no real personality or other traits that they're specifically looking for, and compatibility is tested while characters are pulled into that initial simulation/shared reality. They are keeping very comprehensive files on new arrivals, including physiology, personality, powers, etc. They are, as of now, still playing with the settings, as it were, and are targeting people randomly from other dimensions/universes, testing for compatibility, and then bringing anyone compatible into this universe to their research facilities. This means that every character in the game is compatible with Sylphid reproduction, and susceptible to being 'taken over' by a Sylphid.