... the Pink Agaricus (Atlantica) is a tad annoying because even with 13 MP I found Stopga lasting too short to get in more than 40 to 50 hits even with Aeroga and all combo plus-abilities equipped.
I contemplated ordering Donald and Goofy to attack as well, but I am not sure if their hits even count.
Don't. In fact, Goofy and Donald will only reduce your hit count. Actually, Ragnarok is your best bet, but since you need to press triangle to perform it, you'll end up asking for Goofy and Donald's assistance and they'll screw it up.
You might want to go a few pages back in the main forum and take a look at a thread titled Pink Agaricus Heartless Frustration. A lengthy discussion on good tactics and get-arounds has taken place there. I hope it benefits you.
EDIT: I know a link would've been great, but I'm posting via mobile now and it's quite hard to link. Sorry.