The tools I used included Advance Map to change the maps for towns and buildings and for placing characters and spawn points. For writing the code, I used XSE (eXtreme Script Editor). I had to take into account how much memory each script would take up. Usually 10 bytes allowed for simple dialogue but larger scripts which involved dialogue, movement and battling required a lot more. Occasionally I ran into bugs following my underestimation of just how many bytes would be required, which led to overwriting existing parts of the games and causing glitches.
Upon the release of Pokémon SoulSilver in Japan, I worked on an unreleased texture mod which altered the player's texture to match that of a Team Rocket grunt.