This close to Hallowe'en, I wonder how many doppelgängers are lurking about. The doppelgänger is a spectral counterpart to a living person; similar in appearance, but not alive.
Legend has it that on Hallowe'en, a girl can discover her future husband by completing a small ritual: she must stand in front of a mirror with two candles and a piece of apple in her mouth. The mirror will show her the ghostly version of her future husband, looking back at her from behind her shoulders.
To take it one step further, if the girl walks around a graveyard 12 times, she will actually meet up with her future husband's doppelgänger. While predicting the future is tempting, that's a little too creepy for me.
(Mirror photo from Wikimedia Commons)