Does it crash as soon as it opens? I have not tried it on Sierra. There might be a log file under "~/Library/Logs/MatatoGames/Cat And Capy/Player.log" or "~/Users/{YOUR USER}/Library/Logs/MatatoGames/Cat And Capy/Player.log". I would love to take a look at it if you can send me the file at matatogamestudio@gmail.com :)