For proper operation of the Undertale games on MAC OS needed “Automatic selection of libraries. “
Without this Undertale on Mac may crash, or stoped working at start to fail.
1) Install the program MacKeeper
2) Run and select “Data Control”
3) Next, “Data Encryption” and put a tick in the “Automatic selection of libraries. ”
Save and run the Undertale on your Mac, More problems launch Undertale, you will not.