If you have an antagonist, it should be someone the reader loves to hate. It will be more interesting if he has some redeeming feature or at least feels he has just cause for his behavior. Amoral monsters, used frequently in horror, are less interesting. Personal stakes, even for the antagonist, make the tension higher. In most genres, this character or entity has a goal that is the opposite of the protagonist’s goal. If the protagonist wants to uncover a mystery, the antagonist must be dead set on keeping the mystery unsolved. If the protagonist wants to win the girl, the antagonist must want her for himself or be so opposed to the protagonist’s pursuit that he will do anything to stop the couple from getting together. The antagonist should also have something deep within that drives him toward his goal. The emotion or underlying belief system must be as strong as the protagonist’s for the stakes to be high. He endorses the flip side of the thematic argument. The antagonist ca...