According to Osho, seeing a satanic image in meditation is your own mind projecting an inner 'devilish' aspect onto the screen of awareness. The master or any object is only a mirror. Use the vision as a pointer: meditate on it, recognize the trait within, own it, and consciously drop it, rather than blaming the outside.
If a devil appears in meditation, it’s your own mind showing you something inside you—notice it, find it in yourself, and let it go.