1. Bowser's Castle is indeed a stage, and is based on Mario Kart. Will be shown in Bowser Jr.'s reveal trailer.
2. Shooting Gallery--which is based on a number of light gun games--will also be a stage that will be shown off during Duck Hunt's reveal trailer.
3. The Great Cave Offensive is like a SSE stage, only you still have to beat each other up.
4. Gear Getaway is a stage.
5. Event Matches have been cut as we have known them.
6. Instead, Master Orders and Crazy Orders take their place under Special Orders and essentially carry on that role.
7. Smash World is a board game mode and is the Wii U's equivalent to StreetSmash.
8. Tower of Smash is indeed the main answer to Smash Run.
9. 8-Player Smash is also a thing, though only the really big stages will allow it.
10.Metal Face is a boss.
11.Dyna Blade is a boss.
12.Ridley is shown.
13.The Underworld is a stage, and will represent the classic Kid Icarus titles.
14.Temple will be shown off as a retro stage.
15.Delfino Plaza returns as a retro stage.
16.Isaac is an Assist Trophy.
17.Ray Mk. III returns as an Assist Trophy.
18.Stage Builder will return, complete with Wii U functionality.
19.You get a better look at the Gaur Plains. It's actually a lot bigger than the 3DS version of the stage, complete with some movement.
20.Boss Battles makes it return as a mode. And yes, you even fight Yellow Devil here. To unlock it, you must unlock all the stages, and clear Tower of Smash at least once.
21.Tabuu makes his return as the final boss of Tower of Smash. Both he and Master Core can be fought in Boss Battles.
22.Medusa is the boss of Palutena's Temple.
23.There is no Nintendo Land stage. It's actually Wuhu Island and it is based around Wii Sports Resort. The stage is different every time you play it, though the FD version of it is just a grassy field with the water in the horizon.
24.Forest Haven is also a stage.
25.Chunky Kong is an Assist Trophy.
More to come.
26. A new Pokémon City based in another city. It's essentially just one big amusement park; reminds me of Poke Floats.
27. We are introduced to the 3DS Connectivity features.
28. A number of new trophies are to be shown.
29. Endless Ocean is a stage with a unique physics engine.
30. Tourney is back, and can hold over a hundred players!
31. Rambi is an Assist Trophy who behave just like Gogoat.
32. Sakurai reveals some bonus on-disc DLC, but opts not to reveal the specifics.
33. We are introduced to the Subtle differences in Classic Mode.
34. All-Star Mode will show off the Assist Trophy functionality.
35. Sakurai will reveal that via Wii U and 3DS connectivity, you can unlock all the custom equipment, moves, and characters in the game that you had already unlocked in the previous version.
36. However, you still have to work on unlocking every stage and trophy (the latter, I must ask, why!?).
37.There are about a thousand trophies in this game.
38.We will learn of the third DLC pack.
39.More will be explored concerning Amiibos.
40.Break the Targets returns, and each and every character in the game has their own unique obstacles.
41.All the trophies from Smash 3DS carries over to the Wii U (so again, I must ask; why can't we carry them over from the 3DS version and vice versa?).
42.We get a much bigger look at the options menu. That's where you can see all the newcomer trailers for free.
43. The 50 new things bit is just rounding, and even then, a number of trophies are being counted.
And that's pretty much it, really.