I had figured that out already because I had done a previous stage already that had a similar thing. The purple coin level with all the pull stars in it. It was more difficult just 'cause it's so easy to just make one little mistake.
Although, I might have to recant my hardest level in a few weeks after I finish the Luigi mode. I think I got lucky, but the first Cosmic Comet (where you race yourself) in the Honeyhive galaxy was tough with Luigi. That dude has vegetable oil on his shoes I swear!
Is the the level with the waterfall? I've only did it with Mario but it was easy if you took the right path when running up the first bank. Then doing a long jump over to the waterfall from there instead of running to the bottom of the waterfall and back flipping up.
Can Luigi do the long jump where you press Z then immediately press A?