I think sometimes with dreams. Not only do we have a good angel beside us, we also have a bad one. This devil is the one whose place we will take when if go to heaven. Scripture tells us that one third of the angels fell from heaven at the End of the Great Rebellion led by Lucifer. We are each of us intended to take the Seat of a Fallen Angel and this is the particular angel who strives against us. For instance Our Lady,as Queen of Heaven took the place of the Son of the Morning, Lucifer. We and our demonic foes are mirror images of each other, so just as Mary shows forth humility, Lucifer shows pride. Its like looking at a imag in a mirror, all back to front. We're bound to meet this Dark demonic shadow of ourselves in our dreams.