From the Super Mario Wiki
A Super Leaf is one of the many power-up items in the Mario series. Super Leaves originated in the game Super Mario Bros. 3, where they turn Mario into Raccoon Mario. As such, Mario or Luigi will grow raccoon ears and a raccoon tail. This tail has many functions. A move of the Super Leaf is using the tail the Bros. get to spin nearby enemies by pressing the B/X/Y Button. Second, if Mario or Luigi is in the air, he can descend slowly by wagging the tail. Third, Mario and Luigi can use the tail to hit a ? Block/Brick Block to make the item pop out or break the Brick Block.
Super Mario series
Super Mario Bros. 3
Super Leaves first appear in the game Super Mario Bros. 3. The item transforms Mario or Luigi into Raccoon Mario or Raccoon Luigi (respectively). If they run for long enough, the P-Meter will become full. When this happens, they can jump and fly by holding . They can also float down slowly by holding . If they hit , they will swing their tails, which can activate ? Blocks and defeat enemies.
Super Mario 3D Land
After a long absence, Super Leaves reappear in Super Mario 3D Land; however, they turn Mario into Tanooki Mario, and Luigi into Kitsune Luigi (a.k.a. "Tanooki Luigi"). In spite of the change, the Tanooki forms granted by Super Leaves still act as Raccoon Mario, but without flight. Bowser's forces are given "Raccoon" forms from the Super Leaves he's stolen. Additionally, the leaves in this game were redesigned by being given stripes, eyes and a "bite" mark. They are also tied into the game's plot, rather than just mere power-ups. It is revealed in the game's opening that Mushroom Kingdom's Super Leaves grow from a rare tree called the Tail Tree (on account of its oddly-shaped bough). During a storm, Bowser stole all of the tree's mythical leaves by blowing them up from the tree, using them to power-up his minions and bestowing them with tails to attack and float around. There is also a variation of the Super Leaf in the game called the Invincibility Leaf, that gives Mario a glowing, white Tanooki costume, and makes him invincible. Mario can only obtain this power-up if the player has lost five lives in a level. Another item similar to the Super Leaf is the Statue Leaf, which turns Mario into Statue Mario and allows him to turn to stone for an certain amount of time (essentially functioning as the original Tanooki Suit did, except there is still no flight and the transformation is done through a Ground Pound, lasting much longer). The Super Leaf's new design makes it look similar to the symbol of the Animal Crossing series.
New Super Mario Bros. 2
Super Leaves also appear in the side-scrolling Mario game, New Super Mario Bros. 2, having the same design from Super Mario 3D Land and Mario Kart 7. Unlike in Super Mario 3D Land, they retain their original effects from Super Mario Bros. 3 and turn Mario or Luigi into Raccoon Mario or Raccoon Luigi, respectively. However, Luigi keeps his Japanese fox (kitsune) tail and ears that were first seen in Super Mario 3D Land in his Tanooki Suit, or in his case, a "Kitsune Suit". While in this form, the P-Meter appears in the bottom left corner of the top screen and Mario can run for long enough to fill it up to fly by holding or . He can also glide down by holding or . He can swing his tail with or to activate ? Blocks and defeat enemies. In addition, if Mario loses five lives in a level, a block with an Invincibility Leaf inside appears, just like in Super Mario 3D Land. The only difference is that it changes Mario or Luigi into White Raccoon Mario or White Fox Luigi, respectively. In this form, Mario is invincible and the P-Meter fills up much faster. He can still, however, lose a life by falling into lava, bottemless pits, Poisoned Water or by being squished between two walls.
Super Mario 3D World
Super Leaves make a return in Super Mario 3D World, albeit significantly less common than it was in its predecessor. They are used as they were in Super Mario 3D Land. All characters can touch it to use a Tanooki Suit, or in Luigi's case, Kitsune Suit. Peach and Rosalina have short skirts with dark brown tights. Toad does not have a scarf unlike in Super Mario 3D Land.
Mario Kart series
Mario Kart 7
Super Leaves appear as an actual item in Mario Kart 7. Here, they create a tanooki tail on the back of the kart which doubles as an offensive and defensive feature. Pressing or swings the tail which can hit other karts and protect the player's kart from other items such as Green Shells. However, if the tail was hit by shells without actually spinning it, the tail will disappear. When activated, the Super Leaf lasts for 10 seconds, or until the player spins out, tumbles over, or being a target of a Spiny Shell.
The tail replaces the kart's propeller when used underwater, and it makes air glides longer.
Mario & Sonic at the Sochi 2014 Olympics Winter Games
A single Super Leaf appears in the Mario version of the Dream Event, Figure Skating Spectacular, in Mario & Sonic at the Sochi 2014 Olympic Winter Games. It appears after defeating the False Bowser similar to Super Mario 3D Land.
Super Smash Bros. for Nintendo 3DS / Wii U
The Super Leaf has been shown to appear as an item in Super Smash Bros. for Nintendo 3DS / Wii U. It appears to transforms fighters into a raccoon form, though what effect this has on them is unknown.
Names in other languages