This is a massive tileset that I use to create a lot of my Pokemon deviations! The tiles were not created by me, a lot of them were created by independent artists: Alucus, Kyle Dove, Dewitty and CNC, and collected together by zetavares852!
You can use a program like GIMP to to put it in a 256 x (what ever you want) and then add it to rmxp. Obviously you will have to clean it. If you are making a pokemon game then talk to me I can surely give you some advice with my friends.