- Must be believable. Yes, even in supernatural and horror you want your antagonist to be realistic. They have thoughts, emotions and a goal as well. This is the key. You must know this character as well as you know your protagonist.
- Must have an opposing view from your protagonist.
- Will create problems for your hero. For instance, your antagonist might be the student sticking out their foot whenever the protagonist walks by them. Or changing into a werewolf might cause your protagonist consternation about what he/she will do in that other form.
- What motivates your antagonist? Is it a low self-esteem that makes them lash out at the protagonist? Or is it the call of the full moon? Whatever the motivation-you should be able to get this across to your reader. Not in so many words, but through their actions.
Remember, your antagonist will create conflict for your protagonist. They must be three dimensional, so it helps if you know them as well as you know your antagonist. The antagonist doesn't have to be your protagonists enemy, they may be friends or it may be the situation. Keep it real even if your antagonist is a werewolf.