Mario gains a jumpsuit and a helmet with a propeller. When Mario uses the Spin Jump, he'll propel up literally instead. When in air, Mario can do this one time before he lands. Spinning makes Mario slow down a bit. Mario could also beat foes when using the propelling technique, by spinning fast (the player must do the same as when Mario ducks), which make Mario speed up a bit by falling.
Mario has been able to obtain the power to fly since Super Mario Bros. 3's Super Leaf, and New Super Mario Bros. Wii introduced the Propeller Suit, allowing Mario, Luigi, Blue Toad, or Yellow Toad to propel themselves high into the air and float around. It's a fairly useful ability to have in a platforming game, even if you do need to shake the Wii Remote silly in order to actually fly upwards.