I can do without most of the purple coin challenges. As I've said before on a blog, a purple comet with spring mushrooms = a shit sandwich. A lot of the purple coin challenges I really hate, because if you fall down a pit (which is pretty easy to do when trying to find every single coin), you have to start the whole thing all over again. No checkpoints or anything; you don't start with how many coins you left off. You just start over. It really pisses me off, because some of those coin challenges will take thirty minutes to complete on your first try IF you don't die, and if you just can't seem to find those three last coins in that one stage before you fall into a black hole, then that's 97 coins down the drain. Congrats, you get to spend another 15 minutes recollecting the coins.
Another minor thing I have to complain about is the powerups. You can't carry them through levels, and they're only used to complete certain missions; you can't just loaf around with Ice Mario. Plus, the time limits for Ice Mario and Fire Mario are pretty stupid. I get to sock enemies with a fire punch for five seconds, IF I have that much time after completing a puzzle that required the fire flower. I'd just enjoy dicking around with Flying Mario and Ice Mario where they don't belong, if for no other reason than strolling through levels in a different, more leisurely manner.
Damn, I could go for an Action Replay right now.