Beat 7 special worlds with Luigi and got the crown level. The only challenge is precision jumping because even the slightest tap on the control stick will send you careening off the edge. I don't feel like I'm dying because its hard, just because the movement is kind of iffy when it comes to precision.
I finally beat this god-forsaken game. 9-7 claimed like 50 lives (reset it every time ) because the third star coin in the level is a giant piece of shit and ice physics are the second worst mechanic ever, with water physics being first.