Super Smash Bros on Wii U and 3DS will allow players to customize their favorite fighter's special moves. Each character will still have four special moves, each with two variations, allowing for a total of 12 possible moves. For example, Mario's fireball might fly quickly in a straight line, or cause multiple hits, or it might bounce along the ground as it always has.
The news comes from a Smash Bros event at E3 2014, hosted by series creator Masahiro Sakurai. He pointed out (though an interpreter), that these customized moves will not be available when playing the "with anyone" mode, but you can use them when playing the "with friends" mode. Furthermore, custom characters can be transferred between the 3DS and Wii U versions of Super Smash Bros. When asked how that process would work, Sakurai told Joystiq that we'd have to wait for the Wii U release to find out.
Players will also be able to give their players "equipment" which alters certain statistics, like speed. Different characters will be able to hold different amounts of equipment, said Sakurai, noting that larger characters can hold more equipment, while lighter, more agile characters can't carry as much, to compensate for their other advantages.