I've fought Emerald about 20 times now and after suffering loss after humiliating loss I finally got a working strategy.

I don't know if anyone else has had this but I meat him just as the timer was down to about 3 seconds. It then ticked down to zero while my characters were celebrating.

Anyway, the victory screen came up and starts handing me my Gil and then it starts flicking between that and the game over screen.

The 2 flashed back and forward but in the end the game over screen won and I went back to the title screen!

Hopefully no one else has to suffer this pain.

For anyone who pities me (rather than mocking me for not bothering to get Underwater materia) I have now beat it (using Underwater this time) so it's on to Ruby!