I mainly remember the Zip Slasher with Marluxia, the Invisible in Beast's Castle, and the stupid Dustflier.
Marluxia did hit it a few times, but after hitting once or twice, he would just stand there like an idiot. Sometimes, if I felt like it, I pushed him out of the way
The Beast's Castle Invisible...that was the mission with Axel, right? Axel...ended up dying 3-4 times, but we survived.
And that damn Dustflier. The first time I saw it, I wasn't really confident in my ability to win, and my battery was running low anyway, so I just ran for it. Then I came back and killed it, on the third try, because I was a bit reckless and impatient the first two times. That was the longest battle of my life.
I fight them for heart points because it's pretty much the only thing they're good for.