The Stadium has three mini-games:
Multi-Man Smash
This mini-game has several variants:
10-Man Smash
You simply need to defeat 10 opponents as fast as you can. They're all easy to launch so Smash attacks and dash attacks are enough to send them flying.
100-Man Smash
This is the extended version of the 10-Man Smash. They're all easy to launch so Smash attacks and dash attacks are enough to send them flying. Occasionally, helpful items will arrive via a moving platform overhead. Use these items to your advantage to easily KO multiple enemies with little effort.
3-Minute Smash
You have to defeat as many enemies as you can within three minutes. They're all easy to launch so Smash attacks and dash attacks are enough to send them flying.
Rival Smash
You'll be playing with a CPU-controlled rival. You'll be competing with him/her in defeating as many enemies as you both can. There is no time limit and you only have one stock life. The game will end only if you get KO'd; the total score will tallied by then. You can attack and KO your rival, which is worth three points per KO. However, your rival has infinite stock of lives and can absorb considerable damage before you can launch / KO him /her. Standard enemies can still be launched easily.
Endless Smash
As the title suggests, this will Pit you against an endless horde of easily-launched enemies. The mode will end only if you get KO'd or if you quit the game.
Cruel Smash
You'll face off against a horde of elite Mii Fighters. They're harder to launch and they have enough power to send you flying as well. They're also aggressive to expect them to give you little rest since they won't stop harassing and attacking you.
Target Blast
The objective of this mini-game is to power up a bomb and launch it to the stacked targets and objects on the right-side of the screen. You'll be given two attempts and the score will be totaled afterward. To power up a bomb, you have to attack it to build up its damage percentage. Once you touched it, you'll have 10 seconds before it detonates. By that time, it should already be flying towards the obstacles. The timer will only start when you touch the bomb so it's possible to charge up a powerful attack as your starting hit then follow it up with combos.
Be careful not to extend your combos and make the bomb bounce over the place. At around 4-5 seconds remaining, you should be charging up your smash attack. Hit the bomb from the left side. If done correctly, it will smash some of the objects and detonate in the middle, taking out most of the item stack's supports.
Home-Run Contest
Here, you have 10 seconds to deal as much damage to the sandbag before hitting it with the provided Home-Run Bat to send it flying. The higher the sandbag's damage, the farther it flies. The timer will start automatically, regardless if you attacked the sandbag or not so act quickly!