The Glory Funhouse Mirror

Kind of like an optical illusion, but it's not optical.

When you have a character who you want to make look better than they actually are, you place a Glory Funhouse Mirror next to them. This is a second character who might be similar to your Main Guy, but is worse in comparison, as if to have The Audience say "This guy's bad, but he could be a lot worse" and take more of a liking to the Main.

The Glory Funhouse Mirror can come in many different forms: the Dumbass, a Useless Secondary, and the Rat Bastard just to name some.