http://mariomaker-wp.nintendo.co.jp/
Translation thanks to zellisgoatbond on RedditA few notes, since it's in Japanese:
Click the red button, then select the device type and resolution (the red star should show your resolution).
Clicking the rocket deletes everything (A pop-up box will appear - the right button confirms and the left button cancels.
You can drag some stuff onto others to create unique combinations. Try giving a mushroom to some enemies.


