To dream about the devil suggests poor aspects of yourself. It could also represent a guilty conscience that you have been carrying around with you. You should release these emotions. Also, the devil can symbolize mental acuity, deceit, and astuteness.
To dream that you have defeated the devil indicates that you will overcome your adversaries.
To dream that you talk to the devil suggests that you will endure urges that are difficult to overcome.
To dream that you are friendly with the devil indicates that you could be enticed to perform an act or something that you would rather not do. You could be working through moral troubles.