HOW TO MAKE A BOSS AND HAVE MIRRORS TO MAKE IT HARDER

What I'm trying to say here is how do I make it work like that?. What is the purpose of the bosses having mirror mirror images of themselves, like do they heal the boss or use a skill on the boss to make him harder? I need help on that with a boss in my SOLDIER game.

I don't mean how to make a boss. lol. That seem a dumb title start off.

Edit: Just bumping up again.