I don't agree that Japes is the worst stage for olimar against every character though. The best player in our state is a marth main, Xisin. I ran into him in tournament yeterday and although he won the set, I wrecked him on japes :x And I was the one that CP'd it too lol.
You have to be prepared to play really REALLY gay though.
Here's basically what I did. I went to the right platform, and spammed pikmin like crazy. Marth is obviously forced to approach, but that isnt as easy for him as you'd expect. Say he jumps from the middle platform and attempts a fair. I merely ran to the right, and grabbed the ledge. He then had three options
1) Pull back and land back on the middle platform. If he does this, I merely go back to what I was doing before, spamming pikmin.
2) Grab the left ledge of the left platform. I'm then able to pull back from the ledge, throw a pikmin, then regrab without having to tether. there are other ways to get him off using aerials, but it's pikmin dependant and situational on what the marth does off of the ledge
3)Land on the right platform after the aerial. It's obvious what I did if he took this option. I drop from the ledge, use my second jump to uair him from under the platform, then regrab the ledge without having to use tether, allowing me to do this infinitely until he gets the **** off. If he takes this option, he's forced to switch to either option one or two, in which I'll be able to spam more pikmin easily.
But you don't get a kill until like 180%? Just camp your *** off until they're higher than they need to be for a kill. I often dont go for kills until near 200% on japes.
But the water kills you, right?? If you camp the right side well enough, it's extremely difficult for olimar to die. Marth isnt able to space his attacks well to knock you past the blast zone. And if he knocks you into the water, it's extremely easy to live. If you're use to the water, you can usually time your jump out so that you can basically choose which ledge to recover to. The main problem is that once you do recover, you're much more vulnerable to your oppponent.
So if you're not afraid of playing extra gay, and dont care about people hating you and getting pissed, japes really isnt TOO bad for olimar if you're against a character that can't camp you from the middle platform, or get around your planking.
So I... guess i'm kinda encouraging planking :x