For we are not fighting against flesh-and-blood enemies, but against evil rulers and authorities of the unseen world, against mighty powers in this dark world, and against evil spirits in the heavenly places.
- Ephesians 6:12
There's a world out there a lot of people don't know about, it's a world that is unseen. It's a different dimension. It comes in many disguises: aliens, fairies, ghosts, shadow creatures, etc. Even under the disguise as angels of light. But these are not beings of light, they are beings of darkness. Different cultures have different views of them but most of them view them as mischievous and evil. They are NOT to be messed with.
I'm an avid anime fan and I've seen animes where they had even good demons. This is impossible though. They can appear as good but they are not good. They're crafty, witty, and they have centuries of knowing how to fool us. They use our weaknesses against us. They can come in the form of a loved one that's passed on. If you encounter a "supernatural" being, even if you think it's an angel, test it. How do you test such a being? Use the Lord's name. If you test it in Jesus' name, it will show it's true face.
I have terrible demonic dreams. It's hard to control your dreams, but for the most part, I've gotten to the point where when a demonic being shows up I usually use Jesus' name. It doesn't always go away right away, I often times have to keep repeating it, but eventually it either goes away or I wake up. I've noticed in my dreams when I don't use Jesus' name and I try to take things in my own hands (like I tried to punch a demon once), it doesn't go well, it gets worse.
I don't always know they're demonic right away in my dreams. They don't always show their true forms. Sometimes even in my dreams I have to test them. There was one dream I dreamed of my dead grandmother and she came and visited. I asked her what heaven and Jesus was like and she was just like, "Eh, it's nice, I miss all of you though." None of what she was saying made any sense though. I could tell something wasn't right. So I tested it and when it realized I knew what it was, it showed it's true form...it's ugly self.
These things are not to be messed with. I've experienced them first hand, not just in dreams. They're pure evil. I know others who have had terrible experiences as well with them. There is no such thing as a good demon.
"The thief comes only to steal and kill and destroy. I came that they may have life and have it abundantly."
- John 10:10
Satan and his demon come to destroy lives. But Christ came to give life abundantly. Christ protects his people from Satan. A child of God CANNOT become possessed by a demon. Christ breaks the chains, any stronghold that Satan has over his children. If you are a child of God you have nothing to fear! It says "fear not" 365 times in the Bible, which probably means God was serious when he said it. He must've wanted us to get it when he said "fear not." So when you face demons, don't be afraid, the King is on your side protecting you! But don't be a fool either, it's not your power that overcomes the demons, it's His. Don't go looking for the darkness. Don't go playing with the occult. This is not to be messed with. But if and when you are faced with these things, Christ is with you. I recommend a couple reads: Dancing With the Devil by Jeff Harshbarger and Seeing Ghosts Through God's Eyes by Mark Hunneman, both books you can order on Amazon. I also recommend Laura Maxwell's podcast The Supernatural on Eternal Radio.