Press the green flag then press 5. Restarting? Press green flag twice.
This battle was a request from @letsfight http://scratch.mit.edu/users/letsfight/ You can leave a request too! All you have to do is tell me the Pokemon, 3DS or DS and then who's back should be facing you! Then it might appear on one of my projects! NEW UPDATE: You can now request the game you want! From Red and Blue to X and Y make sure that the Pokemon are from the generation or an earlier one though!