Launch terminal - basic to make apps work enter: sudo spctl --master-disable (if u want to turn it on back -sudo spctl -- master-enable)
Then enter: sudo chmod -R 755 + drag Appp (enter and u can play)
I've also heard that you might need to change some settings in the system to play old Unity games, but I don't have Mac, so I can't help you here. You need to google it.
