The Wild Monster Baiter is a building that you can attract wild monsters to go to your yard. All you could do is to bait a number of wild monsters, then allow your defenses to kill the monsters. This may help test your defenses. You can scare away monsters if you are overly damaged.
Note: All the wild monsters are level 1, cannot use abilities, and are generally weaker. Also, some monsters cannot be baited, like Zafreeti and Vorg.