Okay, some of these challenges seem ridiculous...

[CM30]

I don't own the game yet, but damn...

http://www.destructoid.com/the-super-smash-bros-for-wii-u-challenges-guide-284165.phtml

I mean, having to KO Miis in Cruel Smash to even unlock Duck Hunt Duo? Having to get 8 KOs in Cruel Brawl as Lucina in particular? Beating the hardest version of All Star without healing to unlock things?

They seem kind of sadistic to some degree...

 

[KirbyZ]

I remember when I practice in cruel so much that I got 13 KOs in one fight.   Never again.....

 

[Artisan Vistra]

Well I find it beatable as the Miis have terrible AI and Lucina has counter. I finished that one in Smash 3DS with Shulk's counter instead so that makes me pretty proud. I can see these being possible. Even if they push you to the edge. Oh, and I remember beating All Star on Normal with DK w/o healing just for kicks. Not likely the average player would be able to do these though.