If you play Super Mario Kart enough, you're going to get better, that's pretty much a given. But, what if you get so good at the game that you have nothing left to do? Nothing left to unlock, and the game's just not challenging any more?

Well, you could go to your driver select screen

Then hold Y and press A

Your driver shrinks! Just like he hit a poison mushroom or was hit by lightning. Start the race and:

You retain shrinky status, which means that not only is your top speed lower, but if you get hit by another kart you get flattened and immobilized for a few seconds

You can temporarily cancel the effects by grabbing a poison mushroom, but you'll shrink again when it wears off

How's that for a challenge?