The 3-Up Moon Block is a block introduced in New Super Mario Bros. U and again in New Super Luigi U. It is very infrequent, in secret places that are usually hard to find, and can found by using the Wii U GamePad in Boost Mode. The player must tap on it to make it pop up, and players using a Wii Remote need to reach it to pick up the 3-Up Moon inside quickly before the block will retire. There is a 3-Up Moon Block in every level in the game.
In the Nintendo Switch port, New Super Mario Bros. U Deluxe, they were removed alongside Boost Mode, and 3-Up Moons are instead obtained by hitting blocks containing 1-Up Mushrooms with Toadette.