Magic.yml is an internally-used file that defines all of the 'Magic' values that AntiCheat uses to determine if a player is hacking or not. Since the program is fairly complicated it becomes increasingly difficult to describe these values to a non-programmer, but I've made an attempt to make sense of them all on the AntiCheat Magic documentation page.

Please keep in mind that if you wish to change any of these values it may change the operation of the plugin, and so if you experience an issue that is only made possible by your change I won't consider it a bug. Feel free to ask me to clarify specific values.