Everything should be supported by this core.
Full automatic region selection is implemented. Select your desired region in the menu. If the game does not support your region, it will automatically select the next best one.
3 and 6 buttons are supported for controllers, and theoretically up to 4 players can play games that use J-carts such as Micromachines, which had two ports on the cartridge.
EEPROM saves should be fully supported as well.