People have different interpretations and meanings for when envisioning opponents in a dream. Some meanings include not seeing themselves in a capable role, struggling competition, failing at achieving their goals, concentrating more on what might go wrong than something productive.
In a dream, your opponent typically represents something that you feel pride or superiority about mixed with some sort of limitation. Your opponent also seems to be able to hurt you, invade your mind, control your thoughts or use violence against you when it comes to dreams warning you from danger and other potential physical, social or conscious problems.