UPDATE: The video on wii.com has apparently been updated to remove the faces of Ness, Lucario, Jigglypuff, and others. The images below are, however, accurate, and many people (including myself) can vouch for the fact that these faces did appear in the original movie for an hour or two, at least. That Nintendo has removed them only seems to further confirm that these characters are hidden in the game.

An intrepid GameFAQs poster by the name of Edible has apparently done some detective work and noticed that one of the videos on the Japanese Wii site features the recently revealed sticker power-ups mode. It appears from the movie that different power-ups can be applied to particular characters, and small icons appear for each character on these screens.

Of particular note is that there seem to be small icons for both Lucario and Jigglypuff (next to one for Pikachu and Pokémon Trainer) and Ness (next to what appears to be Lucas); more interestingly, the Pokémon universe characters appear when a Pokémon sticker is highlighted, and Ness and Lucas appear when an Earthbound-related sticker appears. The same holds true for Sonic- and Kirby-related stickers, as suggested by both the movie and Dojo screenshots.

Both of these screenshots can be seen at around 4:20 in the video.

The screenshots, although perhaps ambiguous, do come from an official video on wii.com, and are thus most certainly authentic.

Gimpyfish has posted a video on YouTube that summarizes the find.

We'll have more information as we can get it.