Reflections

Things used to be simple. Reflections used to be just light hitting a surface and showing you what you look like. But then things changed. Now we know that our reflections actually lead to another world. A place where your exact copy lives, only their life is the complete opposite of yours.
Now people have figured out how to cross between worlds. Simply be in the exact same place at the same time as the other you. Then reach through the reflection. For some, this is a dream come true. A place where the poor become rich and the sick become healthy.
One problem- only one you can exist in each world. So how do you decide who gets to keep the better life?
You fight to the death.