Re: Giant Pink and blue mushroom drops help.
Okay I'll tell you what I did since it worked for me (but it did take a few tries).
For Pink Agaricus go to the bottom of the ladder at the tree house and make sure Donald and Goofy are next to you, summon Genie, Mushu, Simba, or Bambi (though Bambi would be best as he can replenish your MP), go to where the Pink Agaricus appears, release the summon and Donald and Goofy will still be on the outside by the ladder and they won't get in your way, then use stop and cast aero (stopga and aeroga preferably) and use Ragnarok. I still wasn't able to get 100 hits on it but with that trick I was able to get 50 hits which is how many you need for the synthesis item.
As for the blue mushroom, you are speaking about the one that you have to keep in the air right? Assuming you are:
Go to Neverland, go to the deck of the ship and try to get one of the mushrooms into a corner, knock it into the air, use aero (though aeroga is best since it lasts longest), and keep casting aero before it stops and hopefully you'll have enough MP to keep it in the air long enough. Now this trick does require some luck as the mushroom may slip out of the corner and you have to juggle it. Luckily for me it didn't do this until the last 4 hits so I was able to get away with it. Hope this helps!