Olimar falls into a pit and loses.
So, anyway, if you did not know, I did test out that you can use your Mirror Shield against Olimar. (I think the Angel Ring will help as well.) If he throws his Pikmin at you, the Mirror Shield will reflect the Pikmin, and they will attack Olimar instead. What this means is that if Olimar decides to use his Pikmin against you, but is attacked by his own Pikmin instead, he
may have to kill his Pikmin and be forced to use Pikmin Pull (neutral B).
Keep Olimar under stress by using Palutena's Arrows. I think this can be useful, since the arrows' trajectory can be manipulated if he decides to duck. Use your shield and grabs. If you grab Olimar, you can toss him up and use the u-air, or you can throw him forward and then fire an arrow. Most importantly, try to get Olimar off the stage. That is his weakness, and we know that Pit is a great edge-guard.