Not sure if this is already in the mod but a feature when Herobrine can crouch-walk up to a player and get really close and personal from behind would be horrifying. Perhaps even some quiet and slow footsteps behind the player would also add to the creep-factor and the feeling that you probably shouldn’t turn around.
Another feature I think would be cool is detecting when the player changes their camera which should cause Herobrine to disappear. detecting which key changes the camera and detecting when that key is pressed or just detecting when F5 is pressed.
SERVER SUGGESTION
#faq channel in the Projects category. Then again, there is a search bar for a reason