Miiverse isn't really the best place to talk about Homebrew or that kind of other stuff(let's say that Nintendo doesn't really appreciate the idea of running nonnative code on your Nintendo 3DS)
You can do a lot more than send messages, if you set several variables for X and Y of other players, you can make a truly interactive world. But that's just basics, there's still a whole lot more than players and messages, once you put in the effort and work, you can make a truly marvelous multiplayer experience.
He would have to supply it via Petit Modem or another way to transfer straight from PC-3DS because since Nintendo owns those sprite sheets and games, they have the right to be able to take down this remake of Mario Maker SB.
Wow, this game has great performance and represents the amazing things you can do with SmileBASIC. Magic Story is an excellent game built on SmileBASIC and I hope many others think the same!