Change what someone dreams about
This is as cool as it is scary: you make a person dream on purpuse and change what a person is dreaming a about.
Studies show that you can bring about a dream in another person. One way is by holding an open bottle of perfume under the sleeper's nose. Another is by whistling. A third way is by blowing air across the sleeper's face with a fan. Someone else can also affect the content of a sleeper’s dream. For example, turning on a light produces happier dreams. And darkening an already bright room can induce nightmares
Making someone stop dreaming is very simple as you just wake up the person. Be careful though, as going days without dreaming has nasty side effects:
dream deprivation produces anxiety, irritability, an inability to concentrate, paranoia, a ravenous appetite, depression, and even suicidal thoughts