I'm taking this with a Ridley-sized grain of salt, but I don't think there's anything here that is completely implausible. In response to some things people DO find implausible:
- 5 characters when the 3DS CSS only leaves room for four: I picture a scenario where there is some kind of 'DLC' button on the CSS that opens a pop-up or new screen. If we're getting DLC characters at all, they won't be limited in number purely because of lack of space on the handheld's CSS. With how long a life cycle this game will have, it would be very weird if a one-and-done set of characters during release window were all that we ever got. Look to MK8 and it's year-spanning rollout as an example of what would probably happen.
- November 21st: I'd put money on this being the US release date, fake leak or not. Too many signs point to this being the date. As pointed out already, Mario 3D World and ALBW both came out on 11/22 last year, which only further cements it.
- Ridley Wings: Wording is weird, but I can see it. "Grows" is probably misleading, I'm guessing he means the wings are just folded on his back while on the ground and stretch out when in the air. Perfectly plausible.
- All Stages/Characters Unlocked: To me, this is one of the bigger indicators this might be the real deal. Nintendo wants this game to have longevity, and the key to that is to have it be embraced by the competitive scene. Within that scene, and especially among organizers, a game that's so easy to pick up and play right out of the gate would be ideal. Also, being able to promote the game without hiding significant chunks of it would greatly help Nintendo's marketing department, who are already in the tough spot of having to ride the 3DS version's coattails. Speaking of which, it would also make the game more appealing to 3DS version owners who want the game but don't want to go through the hassle of starting back at 0. Everybody wins.
On top of that, Smash Tower and the description of the way the Chorus Men are controlled are so very, very Sakurai. I'm indecisive about whether or not this is true, but if it is fake then whoever put it together did a very credible job.
Remember the Bowser Jr./Koopalings leak and how insane the idea of 7 alts for one character seemed, or clone corner on what ended up being the real leak of the final roster? What those situations taught me is that sometimes it's the imperfections and little things people are inclined to scream "FAKE!" at that make a leak look more real in retrospect. There is just enough on here that is either true and weird or too obviously BS that I'm inclined to think it may be the real deal. There's no personalized, desperate attempt at proving validity either (ex. 'My dad's friend works in localization at Nintendo and here's what he told me", or "I can't reveal what I know publicly so solve this macro to break the code"), just definitive claims dropped with no fanfare. If it's a troll, it's a troll who doesn't care if anybody believes him or not. If that's the case, then why even make the effort if you don't know something?