There are 3 things you can do against his pikmin toss.
1. You can Nair them while they're latched onto you.
2. Dsmash them when they're on you or when he throws them but keep in mind it stalls your Dsmash.
3. PKF them when he throws them, Reds will survive this others won't.
There are others that work like dtilt and jab but I like these.
Sooner or later you're going to have to approach him. Nair and Fair will get pivot grabbed. As for Dair i think his usmash clanks with it or something. If he grabs you at low%, you're gonna get about 30-40%. All of them except purples will combo into another grab and then an Usmash.
Once you get inside him jab and ftilt work well since they're fast. Olimar's Fsmash outranges us. I don't think purples will though. Getting utilts at low% leads to an Uair or Nair since Olimar's dair isn't that great. If he gets you above him use Dair.
When he's offstage, DON'T use PKT onless he only has 2-3 pikmin. You'll only give a free way back. His tether with full pikmin is long and comes out fast. His whistle will also beat out anything you try to throw at him. Try to predict the whistle and punish. If he's far enough out that he still isn't onstage with his DJ go for the ledgegrab. If you're at high% time your edgegrab so that he'll go for the tether when you still have invincibility frames or when you go for a ledge attack so that he'll die and you won't either. If you're at low% you really shouldn't worry about it unless you don't won't small damage. If you're offstage watch out for his Fsmash, it has amazing range and it goes off the stage. If you're not careful you'll be using PKT and get extra damage.
Olimar is pretty light so Fsmash kills him early, and you can get Dair dtilt locks early. Olimar's main kill move is Usmash. If you're at kill% WATCH HIS PIKMIN ORDER. It really helps you predict when he will go for an Usmash or Fsmash. Purples kill REALLY early so watch out for those. Purple fsmash range isn't that great so stay out of it's range in kill%.
Some of the different pikmin colors may beat our Fair with theirs. I think our Dair beats their Uair. Our Uair >his Dair.
My Ratio 45-55 or 40-60
Use Nair, PKF, Dsmash on pikmin.
Don't approach with Nair or Fair, you get pivot grabbed.
Space your Dair when approaching
At close range use jab
get him above you for an Uair
Don't use PKT when he's offstage unless his pikmin count is low.
