Single Player Mode details for the 3DS Version.
http://www.smashbros.com/us/3ds/index.html- Classic Mode is undergoing a massive overhaul. Difficulty is determined via a Wager System where you can bet a certain amount of coins to raise the difficulty. The harder the difficulty, the harder the game, and the more rewards you earn such as trophies and character customization options. Anybody that has played Kid Icarus Uprising is sure to know what this is. You can also choose your path for each stage in Classic Mode similar to Street Fighter III: Third Strike.
-Stadium Mode returns with three modes: Multi-Man Smash, Target Blast, and Home Run Contest. Multi-Man and Home Run should be familiar to Melee and Brawl players, though Multi-Man Smash's opponents are now the Miis. Target Blast is a new mode where you hit a bomb towards a tower filled with targets. The more of the tower is destroyed, the higher your score. Think Angry Birds, only in Smash Bros.
and not an unnecessary sell-out.
!In addition, one thing to note about the 3DS' controls.
-All Smash attacks MUST be done with the Circle Pad and A Button. C-Stick attacks are not in this version because the 3DS only has one analog stick and as far as I know the Circle Pad Pro is NOT supported. This is most likely gonna be in the Wii U version as the Wii U GamePad, Wii U Pro Controller, Wii Classic Controller, and GameCube Controller all have dual analog by default.
That's all the info I got.