Smash Balls are going to be a white-hot commodity when we all finally start brawling next year, and little wonder: getting your hands on one will allow you to pull off your respective character's Final Smash, a number of which we've already covered.
But it's not just a matter of walking over the Ball to trigger its powers. First, you all have to beat the absolute snot out of it, with the player who lands the blow that breaks the Smash Ball getting to keep it. Once it's in your hands, a simple press of the B button will unleash your devastating Final Smash, though as Sakurai-san points out in today's update, it's all a matter of timing if you want to create the most destruction possible.
You're advised not to hang around too much, though. In the period between picking up the Smash Ball and launching a Final Smash (when the player enters "Final Smash standby mode"), opponents can still swipe the Ball from your dastardly clutches, meaning some strategic thinking is required.
We're also told about the Pity Final Smash, where a player who is losing badly respawns from a KO in the aforementioned standby mode. Lastly, if you'd rather not use Final Smash moves at all (though goodness knows why you wouldn't want to), you can simply turn Smash Balls off in the options.