First off, I know this was not a full version of the game, but I dont believe this screen will change much from this to the final version. I dont even think the character icons will get any smaller. If you look in the boxes most characters heads barely fit in them, which means the boxes themselves probably arent getting smaller. If you take into consideration the player selection tokens size, which doesnt overlap and will just barely fit 4 selections, and the fact that it characters need to be clearly visible on an original 3DS(which is slightly smaller than a drivers license), youll probably agree that this is likely what were going to see in the final version. At least as far as dimensions go. This is further backed up by a Smash Law, but Ill explain about the multiples of 3 later.
The bottom screen of the 3DS shows what characters have been selected, and has the other options for the game, so there wont be any normal character selection boxes found there. Its not hard to figure out from here that this screen will be 6×4 when filled up. So now youre probably wondering how exactly were going to get a full roster if a single static screen only has 24 character slots; Especially since we already have 36 characters confirmed to be in SSB4.
Well, if we were to flip to another page of characters we would have a second page of 24, which would make for the total of 48. The 48 slots that I now firmly believe were going to have for Super Smash Brothers 4. That makes for 47 characters plus random, or 45 characters if Miis for some reason end up taking 3 slots. Of course this may not be how the screen for the 3DS version works. It could use vertical screen scrolling instead, and that would certainly be a functional option; But 6 still seems to be an important number for this type of screen, and there are some other things to take in consideration from this.
