JOEL - Satan's power is limited. He can do only what he has specific permission from God to do (D&C 121:4; Luke 8:30-33) and he only has as much power over us as we give him when we succumb to his temptations (See Teachings of the Prophet Joseph Smith, p. 187). I haven't heard much from church leaders about Satan's influence on our dreams, so I can only give you my personal opinion. If we strive to live a righteous life, dreams are one way that God uses to communicate His will to us(Joel 2:28-32). On the other hand, I believe if we give Satan power over us during our awake time, it is possible that he also could invade our dreams to further tempt and depress us.