For a very accurate account of what a real demon possession is like, see the movies based on true stories: Deliver Us From Evil and/or The Exorcism of Emily Rose. To see what many demons look like, watch the movie Constantine. I have seen both demons and dragons. All demons and dragons consume hatred and fear as for food. Dragons make great, if not raging warriors; demons are pure evil and like to collect human Souls.
In my limited experience, there are three types of demons in our world: Gargoyles, Shape-Shifters, and the Giant Winged Demons. We all have the garden-variety gargoyles within us. I have had over a handful removed from me already, with more yet to remove. These mostly live within people's bodies and cause pain and suffering and return to us in every incarnation. They are nasty creatures that push us towards doing bad things.
The Shape-Shifters can look like anything, from giant eels to furry monsters to Jesus, and are similar to the gargoyles in threat level.
The Giant Winged Demons, however, are much more dangerous and can literally take over human bodies and inflict physical harm. Your belief system is irrelevant. These are the nasty demons portrayed in movies like the Exorcist, which was also based upon a true story. They can make blood run down walls, levitate people, throw objects across a room, and speak through the victim. Here in the Bay Area, we had one tell a woman to throw her three kids off the pier, where the demon immediately snatched their Souls as they each drowned. Just because you hear a voice telling you to do things does NOT mean it is a good entity, or that you should listen. Many demons have been brought into homes via a Ouija board. Never own, play with or use one, ever.
Dragons are not as dangerous as demons. All the ones I have ever encountered have been huge, pitch black with large scales, and very intelligent. They are loyal and battle ready, but are of little use in a modern society. They love battle violence and were essential to the survival and success of many warlords. Genghis Khan had many dragons, Hitler had many demons.
All creatures of the underworld, including demons and dragons, answer to Satan. However, a well kept shaman secret is the following: Since the advent of the new millennium, Satan has rejoined God and moved from being a fallen angel back to being in the service of the Light and the love of God. Those in the know now refer to him as Lucifer of the light. I was once in the same room with Lucifer and he is just not that scary anymore. But...
The giant winged demon that attacked me years ago was really scary. My Guardian Angels woke me up and quickly told me to get up, light a fire in our fireplace, burn some sage sticks, and chant over and over: "Burn, Burn, and Never Return." It worked. A good demon fighting kit includes wearing a pure silver cross, owning a leather-bound Bible, putting salt across your doors, burning sage, stocking Holy water in house, and always remember that pure love is stronger than pure evil.