The point of the "Bloody Mary" ritual is to stare at your own reflection long enough that Mary comes out and attacks you after her name is repeated three times.
The truth is, the "Bloody Mary" myth taps into a curiosity of the human brain. When we stare at a single point for long enough, our brain begins removing the unecessary detail and focusing on what's important. During the day, this substitution goes completely unnoticed.
When you stare into a mirror long enough, your brain starts removing the erroneous details of your face, resulting in an optical illusion that distorts your face.
You can do it with any reflective surface.