Black Mirror Magick, is something Ive been doing for a while. First, you are going to need a black mirror. It can be small or large its up to you and what fits with your current situation.
You can purchase a nice black mirror from places like etsy or you may create your own. You can take something as simple as a basic 5 x 7 picture frame and paint the glass black. Instant black mirror.
I chose to annoint my black mirror with dark arts oil that I purchased from an etsy shop. You can do the same by annoiting your mirror with your choice of oils.
Dedication. You may choose to dedicate your mirror to your choice of deity/spirit. That is fine.
I burned sage around my mirror and allowed it to sit out under a full moon.
Now you can use your mirror for divination. Its great tool for that. 
I however like to be creative with my black mirror and send things through my mirror or pull things to me.
One trick of mine is to send spiders from my mirror to go through anothers mirror. You can do this even if you dont know if they have a mirror or not. It just seems easier to lock it into the mindset if you know they do. 
I sent spiders, black widows from mirror to another. I used a brooch of a spider to get the image set in my head and then transformed it a bit to.a black widow. I then sent a large group of black widow spiders from my mirror to my targets.
The idea was to ‘love them like a black widow’ as in female black widows eat the males after they mate.
The thing is to keep the imagery in your head and stay focused. Until you complete the work. The best way to do this at least for me is to light a candle close to or infront of my mirror and then focus on the flame. Allowing myself to go into a trance state. 
You want to feel yourself speaking to whatever your sending through and feeling it go through the mirror. See it reach the other side to your target and go through. Visualize it carrying out your intent. In my case with spiders biting my target and poisoning them.
You could also program the spiders to be vamperic and feed you the energy source of the target.
You dont have to be baneful though, perhaps you want to cheer someone up you could send butterflies 
or something else pleasant. You could send much needed energy to someone this way if you wanted.
Once you finish your work you should cleanse the area and your mirror however you prefer. I generally burn some sage and softly wipe my mirror down with a bit of annointing oil. Make sure you close mirror. Much like closing and cleansing a circle. You dont want anyone sending you black widows. 
You could just say something simple to set the intent that your mirror is now closed.
Make sure you dont leave any negative energy around to later affect you. Keep your space and mirror cleansed.
I did use my spiders in a vampiric way and used red juice in my chalice to invision my targets blood. You may or may not choose to do so. 
Happy Magick Mirror Workings!
Halloween would be a great time to experiment! 
