You can make new tilesets, if that's what you're asking... but, they're not exactly sprites. You can put whatever you want in them, all though you can't interact with the stuff beyond what the JJ2 engine is all ready capable of doing; for example, someone out there invented the idea of vertically moving vines in hotel tilesets, which, all though wasn't a new object with new sprites and new engine capabilities, was a new idea and all most like sprites. That's probably not what you're asking, though.