Includes actual character balance changes.
A patch for Super Smash Bros. for Nintendo 3DS Version 1.0.4 is now available in the Nintendo eShop. The official patch notes state that adjustments were made to the balance of the game and to make it a more pleasant experience. This patch is required for online play.
A full list of character balance changes has not been officially released, but testing has shown some major changes. Examples include an increased amount of time for Rosalina's Luma to respawn after death, and suiciding with Bowser's over special attack no longer grants him the win.
The fact that there are balance changes means that old replay data will no longer work once the patch is installed. Also, when playing locally both players will have to be running the same version of the game in order for it to work.