Nurio,
The demo only has 5 characters: Mario, Pikachu, Link, Megaman and Villager with only 1 playable stage. Settings can't be changed so there are no spoilers in the Demo.
How is the framerate and performance? Is it stable? And does the chaotic action work well on a small screen? Are the controls okay with the 3DS setup or restricted?
I played a game with 3 CPU's lvl 9. Couldn't get the game to lag or drop framerate even with 2 items on the field (a pokemon Staryu and party ball). Interestingly the partyball did not drop any more items and as of yet, I haven't been able to get more than 2 items on the field at the same time with 4 players active.
The game feels very smooth and everything is restricted. It works very well on the small screen (playing on XL) but I'll have to add that there isn't something like C-Stick functionality, so if you're used to the C-Stick you're out of luck.
The game is floaty, be prepared for Air game, something that done better than it was in Brawl.