Will Funduino Joystick Shield work on a Mega?
The shield will work on Mega, except of the SPI connection for the nRF24L01 connector. The shield expects SPI on pins 11, 12, 13 and Mega has them on 50, 51, 52. Other shields use the SPI pins on the ICSP header to have compatibility with different boards. This shield doesn't connect to the ICSP header.

You can wire the nRF24L01 to SPI pins on 50, 51, 52.