Don't know if there is a Super Mario 3D World thread, but I'm guessing that there is not. My girlfriend and I dug deep into that amazing game this weekend. We don't do co-op (it's definitely better than previous Mario co-op, but I still feel like it just encourages murder just the same, particularly when trying to collect shit), we just take turns, and she tapped out in Star World. Since then, I have finished half of the special, post-Star world, and up to now, have all of the flagpoles and all of the stamps. I don't know if my endurance can hold to get all of the green stars and unlock whatever the final (I'm assuming?) thing is, but we'll see.
Just absolutely love the game though. Brimming with imagination and the music is incredible.