So as the title suggests, the RPG would be a Pokemon one. Entirely new region I have crafted myself from the actual Cities/Towns to the Gym Leaders and Elite Four.
To explain the "Mature version" part, basically as long as the content is not overly gruesome or sexual, pretty much anything can fly. In a way, look at it as if Pokemon were more realistic. Villains could be allowed to be more menacing and the Pokemon themselves can as well. So if you approach a wild Pokemon that is known for being aggressive? Feel free to make an intense fight scene occur where like a Nidoking literally has its horn stab into a Charmander's stomach for example.
Again, the aim is not to be bloody and gruesome, but to not have this be some kiddy and campy thing like the show is known for being. That said, though, feel free to do kiddy and campy stuff if that is what you prefer.
For detailed information about the RPG, please check the following link which will bring you to the Advanced Interest Check section for RPing. It has bios for established characters, cities, as well as the rules and information on how things like TMs would work, and what classes you can play, etc.