From the Super Mario Wiki
Mario in the air after using the Spin Block
Spin Blocks are platforms that are found in New Super Mario Bros.. When stepped on, Mario or Luigi will start spinning and will fly high into the air, then glide back down slowly, allowing the Bro. to travel longer distances. Pressing the down button on the D-Pad while in the air causes Mario and Luigi to perform the Drill Spin, which has the ability to destroy Brick Blocks in a row or just to descend faster.
Spin Blocks are also found in the Mario vs. Luigi 2-player mode. It only appears on the ice level, where a Star will eventually appear. There are however always coins hovering above the Spin Block.
The movements Mario or Luigi make when they jump on the Spin Block is similar to the movements they make when they use the Propeller Mushroom/Propeller Block in New Super Mario Bros. Wii.
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