The following instructions are heavily inspired by /u/uhohohdear. I modified uhohohdear's instructions and then added support for Retina/HiDPI displays and instructions about how to update MTGA.
- Your macOS/OS X version must be 10.8 or greater
- Your Mac must support OpenGL 4.0 or greater (you can find out whether it does here)
- You must download the Magic the Gathering Arena Windows executable
- You must download a custom Wineskin wrapper [mirror]