For some reason, here's some guy from the Netherlands who has another bunch of Japanese in-store demo videos. Mostly focusing on Pokemon Trainer, and from it we learn that you can choose which Pokemon you start with. See:
Another interesting video, confirming some of my suspicions. Yep, when you don't have a second character in a Subspace level, the second player becomes a different-colored version of Player 1's character.
And was that Super Mario Bros. 3 Doomship music I heard? Neat.
Also, in another video, it shows that when King Dedede gets the Hammer, he actually uses that and his hammer at the same time. Awesome.