>>235887794? I can only remember 2 of them being really tricky off the top of my head, Charizard the first time, and Steelix. All the others are not as much of a pain, but if you're inexperienced, they may still stump you for a while. They include Flygon, because you have to be flipping fast to do it, maybe Salamence because you have to be observant to circle it that many times, and maybe the final boss if you're not prepared, which if you're smart, you should be. I think a lot of people also fret about the lead up to the final boss as well, since it involves a ton of junk running around the screen and firing off a dozen different attacks at once.