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. 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 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.

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 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.

Captain Toad: Treasure Tracker
Super Bells can be seen again in the ending of the Wii U version of Captain Toad: Treasure Tracker, since the Super Mario 3D World intro scene plays at the end; however, the items are not obtainable in the main game.

Mario Kart 8 / Mario Kart 8 Deluxe
In Mario Kart 8, the Super Bell is the emblem of the Bell Cup and a track called Super Bell Subway as a part of the Animal Crossing × Mario Kart 8 downloadable content pack for 2015, and available in the main game in Mario Kart 8 Deluxe.

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 level style.

Other Appearances
Super Bells replace the original game's Bells in the Super Mario Mash-Up Pack of Minecraft, but without the eyes.

Super Mario 3D World

 * Instruction manual description: "Transforms Mario into Cat Mario."

Trivia

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