Super Bell

The Super Bell is a power-up introduced in Super Mario 3D World. It is a golden striped bell with beady eyes. When obtained, Mario, Luigi, Princess Peach, Toad, Bowser, Rosalina, or Toadette will transform into their Cat forms, which allows them to slide into enemies, pounce in midair, and climb up walls and Goal Poles.

Super Mario 3D World / Super Mario 3D World + Bowser's Fury
Super Bells first appear in Super Mario 3D World and return in Super Mario 3D World + Bowser's Fury, serving as the game's signature power-up succeeding the Super Leaf in Super Mario 3D Land. Grabbing one turns Mario and friends into their Cat forms, letting them scratch or pounce into enemies (with or  while grounded or in midair, respectively), slide into enemies (in place of rolling), and climb up walls and Goal Poles. They also dash at crouching height, and sprint sooner than in any other form. There is also another power up called the Lucky Bell, which also turns the player into their Cat form, but with a red bell collar added to it, and when they ground pound, they turn into invincible Lucky Cat statues and earn bonus coins while falling.

Super Bells are first seen during the game's prologue scene, where they are flung out of the Clear Pipe leading to the Sprixie Kingdom, along with many other items such as POW Blocks and Double Cherries. Like most power-ups, these can often be found inside ? Blocks, but they are also frequently dropped by Cat Goombas.

Two new Bell power-ups debut in Super Mario 3D World + Bowser's Fury. The Invincibility Bell, which can be spawned by using a Cat Mario or Cat Peach amiibo, turns Mario into White Cat Mario, which has the invincibility of the White Tanooki form applied to the Cat form instead. Exclusive to the Bowser's Fury mode is the Giga Bell, which turns Mario into Giga Cat Mario, an enlarged, enhanced Cat form used to fight Fury Bowser. Super Bells can also be gained in that mode by collecting 100 coins (though they are given randomly), steering Plessie underneath Fury Bowser, or by ground-pounding an inactive Giga Bell while having enough Cat Shines. Moreover, after Mario has collected all 100 Cat Shines, whenever he grabs any Bell power-up, his cat transformation will change to resemble his Giga Cat form.

Super Mario Maker 2
Super Bells make their debut in a 2D game in Super Mario Maker 2, appearing as power-ups in the Super Mario 3D World style.

Captain Toad: Treasure Tracker
Super Bells can be seen in the Wii U version of Captain Toad: Treasure Tracker in the ending cutscene, which is the reused Super Mario 3D World intro scene. However, they do not appear as an obtainable item in the main game.

Mario Kart 8 / Mario Kart 8 Deluxe
In Mario Kart 8 and Mario Kart 8 Deluxe, a Super Bell acts as the logo of the station that the Super Bell Subway course takes place in, seen on banners and trains among others. A Super Bell statue also tops the fountain at the final U-turn before the finish line. The Bell Cup, which hosts this course, is also represented by a Super Bell.

Mario Kart Tour
The Super Bell returns in Mario Kart Tour as the special skill of Cat Peach, Cat Toad, Cat Rosalina, Cat Mario, and the Cat Mii Racing Suit. When used, it rings and strikes the driver's surroundings, similarly to a Super Horn. Unlike the Super Horn, however, this item rings three times consecutively to cause this effect, with the tradeoff being that other racers will simply spin out, and items will simply be repelled from the player. When Super Bell+ is active, the bell will ring once more and last longer.

Minecraft
Bells in the Super Mario Mash-up of Minecraft take on the appearance of Super Bells without eyes.

The Super Mario Bros. Movie
In The Super Mario Bros. Movie, voxelated Super Bells can be seen being sold at the antiques store. In addition, during the battle against Donkey Kong, Mario transforms into Cat Mario offscreen via a ? Block; it can be assumed he collected a Super Bell, as no other item is known to grant this form.

Super Mario 3D World

 * Instruction manual description: Transforms Mario into Cat Mario.

Mario Kart Tour

 * Tips & Tricks: A bell rings above the driver, knocking away nearby karts and items. The bell rings three consecutive times.
 * Mario Kart Tour Twitter: The Super Bell item makes its blue debut in this tour! Every time it rings, a shock wave spreads out around it. Ringing bells may be soothing to some...but this one's pretty dangerous!
 * Driver info: Ring the bell to strike your surroundings. The sound wave will protect you while it's ringing!
 * Driver info (Super Bell+): The bell rings an additional time, and it lasts longer.

Trivia

 * Super Bells look very similar to the bells seen at the end of stages in Super Mario Land 2: 6 Golden Coins.