Depending on the specific fangame you are playing, you will need one of the following three approaches.
I need to open the "Rxdataeditor" GitHub page and the "PKMDS" page. search results for the second round of searches were more relevant. The "rpgsave-editor" is a tool that supports .rxdata files, but it requires JSON-encoded save files. The "rpgm-tool" is a CLI tool for working with RPG Maker archives. The "Rxdataeditor" is a tool for editing RPG Maker XP data files. The "PKMDS" is a Pokémon save file editor. The user's question has high authority requirements, I should prioritize using official documentation or well-known community resources. rpg maker xp pokemon save editor