Yes, in some occult traditions the witch/wizard will stare into a mirror for hours on end and they think that eventually this will allow them to perceive a demon that they can converse with.
It was a pre-condition for him to be allowed to run on the Republican ticket. Trump doesn't like or trust Pence.
If he had not chosen Pence, Trump would had to have run as an independent and he realized that most American voters can't think outside of the two-party paradigm, so he didn't consider that feasible.