This is a real life incident about a relative, who dabbled in the black arts and paid a very heavy price for it. My sister was married to a Muslim guy and his aunt was highly interested in mastering certain practices mentioned in the Koran, which if done correctly can allegedly give you a lot of powers.
Muslims believe in the concept of Jinns, which are powerful supernatural entities and there are good as well as bad jinns. There are Suras (chapters) in the Koran which outline the procedure for capturing and enslaving these jinns. Apparently it is a very dangerous procedure as it has to be performed by the person when he / she is alone and the complete procedure stretches over several days, for a few hours each day.
Obviously the jinns are not very happy when a person tries to perform this ritual and they will try their best to scare that person. Getting scared and/or leaving the procedure half-way through is one of the worst things one can do, as failure to complete it will lead to the death of the person or result in him/her becoming mad or possessed. Therefore only a brave hearted person, who has enough faith in himself and God should ideally attempt this.
Even after the ritual is successfully completed and the person has managed to capture a Jinn, he/she has to exert a lot of control as otherwise the Jinn can turn against its master and kill him/her. One has to read the Namaaz five times a day, keep Roza (fast) and observe other strict religious disciplines to keep the Jinn in control. The Jinn will implicitly obey its master and do whatever is asked of it. As it is a supernatural being, the master will no doubt become a very powerful and rich person, but he/she is expected to use the powers for the benefit of others.
All this I have learned from my Muslim friends and I hope my other Muslim readers can verify what I have mentioned here.
Coming back to my story, this lady (my brother-in-law's aunt) was somehow fascinated with this ritual and wanted to perform it. All this happened 30-35 years ago, when she was quite young and nobody knows why she wanted to get involved in something so dangerous. Maybe her youth and naivety made her oblivious to the risks or she was bored and wanted to do something exciting... Or maybe she craved for the powers that would be hers once she completed the ritual.
Whatever the reason, she did not inform her husband, as he would have certainly forbidden her, and she practicing it daily when her husband was away for work. At first, it went smoothly, but gradually she started encountering paranormal phenomena such as seeing shadows and hearing whispers all around her, smoke or mist pouring in from everywhere and shrouding her, unbearable changes in temperature both hot and cold etc. Though she was frightened out of her mind, she continued her pursuit until she crossed the point of no return, when these events intensified. She started seeing demons all around and hearing their frightful screams and whispers. To cut a long story short, one day she could bear it no more and fainted out of fright in the middle of the ritual. (This part of the story was coaxed out of her later by her husband and other relatives, but she was often incoherent and there were huge lapses in her narrative)
When her husband came home and saw his wife lying senseless with the holy Koran in her lap, he at once guessed what she had done. He had however no idea how far she had gone. She suffered from high fever for several days and was almost at death's door more than once. Needless to say the procedure was disrupted and she was never able to complete it.
When she became well again, her family members noticed a huge change in her behaviour. She used to be very cheerful and friendly, now her demeanour changed to cold and calculating, even sinister at times. She would no longer laugh and enjoy with other women of her age, but sit silently brooding for hours on end. Often her family members would catch her glaring at one of them malevolently. She would lapse into periods of insanity and then she would order others around in a male, guttural voice. Once her mother-in-law had the shock of her life when this lady assumed the voice of the old woman's late husband and ordered her to fetch a glass of water. Even her husband and her children were scared to be alone with her.
On one occasion my sister was alone late one evening and she was waiting for my brother-in-law, when this lady walked into her house and announced that she would stay with my sister until her husband returned. As many of my brother-in-law's relatives (including this lady) lived in the same building this was not unusual, but my sister had only been married for a few months, was pregnant and she had heard about this story from her husband. Needless to say she was scared out of her mind and quite relieved when her husband returned shortly.
I heard about this incident around 19 years ago and it has been many years since my brother-in-law has passed away. I do not know what happened to that unfortunate lady and if her strange behaviour still persists.