From the Super Mario Wiki
Retrieved from "https://www.mariowiki.com/index.php?title=Blue_Ring&oldid=2800196"
Blue Rings are objects found only in the expansion pack of New Super Mario Bros. U, New Super Luigi U. They appear in levels Dragoneel Depths (Sparkling Waters-5), Ice-Slide Expressway (Frosted Glacier-5), and Rainbow Skywalk (Meringue Clouds-3). When jumped through, Blue Coins will appear for Luigi, the Toads and/or Nabbit to collect, and all coins will turn into Brick Blocks (and vice versa), making them very similar to P Switches that also appear in the New Super Mario Bros. series. If the characters collect all the coins before they disappear, the audience will applaud. Unlike the Red Ring and Green Ring, in addition to the ticking sound effect that plays while the coins appear, the Switch tune also can be heard.