I am basically 100% sure that this leak is real.
First thing is the eye-catchingly strange selection of characters. These characters would fit perfectly into the kind of stuff Sakurai usually pulls, and i definitely see Duck Hunt as being a legitimate character choice for the games big wtf character. We see all the Original 12 and everything. Beautiful.
However, like people have said before, the fact the roster looks so jumbled is likely because there are still 5 characters who have yet to be unlocked. This would also explain the bland-ass background: whats the point of having a background if the entire screen is covered with the CSS?
As far as i've heard people are thinking the 5 rumored DLC's are the remaining 5 slots, but i've been informed that this may not actually be the case. I heard another leak from somewhere that actually came out way before this one. It had a roster nearly identical to this, but with 5 other characters: Ridley, Mewtwo, Dixie Kong, Impa, and Mach Rider. Here's what was repeated to me:
"Neo Zero is a member on Smashboards who apparently has connections with a Nintendo representative.
Weeks before this whole leak surfaced, he was given information about a possible leak having to do with Smash 4.
The character roster was identical to this leaked one except it also included Mewtwo, Ridley, Dixie Kong, and Impa.
And then earlier last week he was told by the same person Mach Rider was also going to be in.
The Chorus Kids were also mentioned, but as part of DLC."
Take that for what you will, since i don't actually have screenshots to show, but it sounds like a believable final 5 to me. Ridley and Mewtwo for obvious fanboy reasoning, Dixie Kong is quite a believable new DK rep because of her constant reoccurance in the DK series, more-so than K. Rool at this point. Impa is the second most reoccuring character in the Zelda series besides Tingle, who was already deconfirmed. She would definitely be a believable new Zelda rep, which we most definitely should be getting by now. Then there is Mach Rider. While he seems like a totally ridiculous choice, So are a lot of the others on this roster. Mach Rider is not an entirely unbelievable decision for sure when we have the likes of Duck Hunt and Dark Pit. NOT TO MENTION, Sakurai, back in the Melee days, expressed that he actually quite likes the Mach Rider character. Perhaps he still has this view and finally found a way to implement the Rider into Smash.
I also believe that along with those 5 characters being the ones not seen, we could actually still get those 5 DLC characters.
I imagine that the DLC characters were still meant to be in the game, but Sakurai did not have them at a high priority to finish. Lucas, Wolf and Snake were likely originally planned for the final build but were not able to be finished in time. Lucas and Wolf especially were likely lower priority, and Snake was undermined by Pac-Man and Mega Man. The Ice Climbers were likely left out until DLC because they may have been somewhat complicated to put into the 3DS build because of them being two at once, so i could easily see them needing extra time to get them to work. Chorus Kids are probably there because they were originally a planned newcomer but were deemed a lower priority one by the other more anticipated ones, such as Mewtwo and Ridley, but he still wanted them in the game. If people would be wondering where the DLC characters would be put, it is possible that they would be selectable in a similar way to the Mii Fighters, in a seperate thing. At least for the 3DS version. That, or the roster will just increase in size on the screen.
A bland background is not all that strange when you think about how the entire background screen is gonna be covered with characters. You wouldnt even be able to see the background.
And of course, the stage thing. I think that along with what was shown for those, that the fact that it shows things that were confirmed that we didnt even know about only makes this more believable.
That's my rant about this for now i may post more later haha