Nintendo released a demo for Smash Bros. 4 on the 3DS to Club Nintendo Platinum members last week. Pandemonium in the Smash Bros. community ensued. It's a relatively small piece of the game -- five characters, one arena, two modes (solo or group), and a little sandbag action during loading times on multiplayer matches. Don't let that fool you though. It's still got enough content to keep you busy for days, maybe weeks.
Last week's version of the demo has unlimited plays. The public demo releasing on the eShop tomorrow morning does not. That's going to be a problem for a lot of you. Unless you plan to keep the demo running on your 3DS until the game comes out on October 3, chances are you'll run out of plays before you've gotten your fill.