New Super Mario Bros U: lava waves

I was stuck on a level last night for ages - I must have lost over ten lives, but luckily there were loads of coins available to rack up extra lives, particularly in the room with the second star coin. Getting to that wasn't that easy - you had to go up the second green pipe in the screenshot, which involved waiting until the platform had raised to its peak, avoiding the waves of lava, and bouncing off the dry bones. I did that many times in the end, dying later in the level or on the boss.

The sign of a great game though - at no point did I think it unfair or want to give up.