Alternative Smash Attacks is a feature introduced in Super Smash Bros. for Nintendo 3DS and Wii U. It was added with the update 1.0.5.
They work exactly like normal Smash Attacks, but instead of using the circle pad (3DS) or left analog stick (Wii U) and the Attack Button, the player can use the Normal Attack Button, which is by default A, and the Special Move Button, which is by default B, together, meaning if pressed simultaneously, they will allow the player to do Smash Attacks. The circle pad can be used while using this feature to use the Up Smash and Down Smash. The character can also be on crouch position to do the Down Smash Attack using this feature.
It is similar to Super Smash Bros. Brawl 's feature of the 1 and 2 buttons pressed simultaneously to do a Side Smash.
This feature was added in order to prevent the circle pads of the 3DS to be destroyed while playing the game. It was also added to the Wii U version.
For more, select Games & More, then go to Options and select Controls.