So, here's one of my bad experiences:
This was about 10 years ago. A friend of a friend of a friend styled himself a wizard or something, and had started a little group of followers who thought this guy was the font of psychic/occult knowledge. I'm not sure what all they did, but from what little I saw of them, I'm sure they were the "take the ouija to the graveyard and burn black candles" sort of experimenters.
The group planned to have a gathering, but due to bad weather (these were not outdoorsy types), they had moved the gathering to the apartment where my friend lived (he was a roommate to one of the wizard's followers). My friend, who isn't really into this sort of thing, had a bad feeling about this and called me, as he knows I have had some experience with psychic stuff. So I stopped by the apartment, as if we had planned on hanging out that night.
The wizard welcomed us to participate. Since the apartment was in a modern complex and was an open plan, it would have been hard for him to exclude us, as my friend and I were hanging out in the kitchen. The first floor of the apartment was the common area, and the bedrooms were in the basement. The kitchen had a little counter/bar that opened into the dining/living room. There was a stone fireplace on one wall. (Remember that, it's important later.)
Some of the group were in robes of various sorts, others were in jeans and shirts. The wizard grumbled a little about the setting - since it wasn't a graveyard, he didn't think we'd get many results. They had a little business type meeting--when the next gathering would be, that sort of thing, then they set up the ouija board (just the regular toy store Feld model), and lit candles and turned the dimmer down on the dining room light. So it was dim, but not dark, things and people were still quite visible in the room.
So the wizard cuts his circle (one version of making a protective barrier around the ouija participants - also sometimes considered a way to keep the energy focused inside the circle). In his best Grade Z horror movie voice he chants a bunch of stuff, I no longer remember exactly the words, but the usual remarks about Speaking To The Dead, and then calling upon some demons and assorted other bad ass evil type stuff. I remember thinking this is not going to be good, if he actually calls something up. He took his place at the board and he and three of his group work the board. Nothing spectacular, the usual gibberish, with the secretary trying to write stuff down & make some kind of sense of it. I'm not sure how long this went on, I was not really paying attention.
At some point, though, I felt the atmosphere change, as the cliche says, the air seemed heavier. At the same time, the pointer goes nuts and flies off the board. They put the pointer back and Something has a conversation with us via the board. Now, unlike the movies, it wasn't Eeeevil, it was just Something Not Nice, something you didn't want to be around. At first the wizard dude was eating this up, he was getting good results, after all. They asked some questions and got rude non-answers. Then someone asked the stupid question, about when they were going to die and the Something said - ALL DIE NOW.
At that point, one of the girls kind of freaked, and the wizard frowned and commanded the Something to go. Well, of course, it didn't. They tried the Goodbye routine and the pointer flew off the board again.
And, now, the Something was walking around the room, around the circle. It wasn't exactly footstep sounding, but definitely the noise of something moving around the room, especially on the stone fireplace--the base was big enough to walk on--and strange scraping noises came from the base as the Something moved across it. The wizard dude was sweating now--his horror movie studies hadn't really prepared him for this. They tried holding hands in a circle (to give the wizard more power), and we all stood there, holding hands, while the wizard dude tried some more incantations.
Everyone was pretty wound up by this time, especially since it didn't work. One of the girls who also knew me, turned to me and said I should do something. (Why she would expect me to be able to deal with something her wizard dude couldn't, is beyond me, but I didn't want to stay here with the Something either.) The wizard stammered something about how my energies wouldn't work properly (which was true--I am not in tune with those who call upon evil for their 'power'.)
But, in a semi-darkened room, with a bunch (8? 10?) panicky people, what did we have to lose? Now, what I did is not in any book about ouija or psychics or anything, it was just what seemed like the thing to do at the time. I had the wizard & the original three people get back on the board, and had the other people stay in a circle holding hands. I put my hands on the shoulders of one of the people on the board (not the wizard dude), and asked the Something to go home. The pointer went to 'NO'. I said something like 'You will leave, now!" and sent energy through the person I had my hands on (I picture it as sending an electric current from the top of my head and out my fingers.)
All of the people on the pointer jumped and said 'ouch!' and the Something was gone. They got back on the pointer and closed the board with the goodbye, closed the circle and turned all the lights back on.
Why was I able to make it leave, when the person who summoned it couldn't? I don't know. I do know that this particular group did not learn a lesson from this, and continued to 'dabble' (as the anti-ouija forces would have it) in ouija and other psychic/occult practices, and, from what I hear, had some other bad experiences. And, whether it was from the oujia experiences or because the psychological dynamics of the people in the group, several people in that group later had terrible things happen in their lives (suicide, drug abuse, that sort of thing), but others have had just the usual things of life happen to them. So I wouldn't blame the bad night of ouija board for the trouble, but, on the other hand, it could have contributed.
Again, like so much of psychic/occult phenomena, there is no cut and dried answer: This was bad; This was good. Every person has their own experiences, and some people do experience the ouija as the source of evil in their life. And others never experience anything on the ouija, other than a fun party game. Shrug. I don't have the answers for that one (or any other one, most likely!)