feltcat

1. Launch Retroarch 2. Launch your mame game 3. Press "Shift+TAB", this should open the mame menu 4. Select "Input (General)" 5. Select "User Interface" 6. Scroll down until you see "UI Cancel", this should be bound to the escape key 7. Press enter, and then a key to set a new binding, if you wish to unbind this option completely, do not press anything for about 5s. You should now be able to use ESC to exit MAME in Retroarch without popping into its weird bios menu.