There's not a particular reason to pick Zero over Pikachu here. He's looked weaker than him for the last two contests. Zero over Yoshi is much more doable due to the very distinct possibility that Yoshi is overrated, but even then I still think he's looked a little better than Zero. I think Yoshi could beat that result on Auron. It's not guaranteed though, and Zero>Yoshi is definitely a worthwhile upset pick although you should have Pikachu here anyway.