Arrow keys to move, z to shoot. Glitches can sometimes occur if you don't press the green flag twice.
The script to stop the player from escaping the box is from BBOP13, and the Mettaton Neo sprite belongs to Toby Fox. This is possible, and I HAVE beaten it! Although it seems like Mettaton has ridiculously high amounts of health, you can move in closer to rapid fire and deal more damage. And if you've ever played the Sans fight, you should know how to do the final attack :)
