The axe (or ax) is an item found in the castle levels of the original Super Mario Bros. Mario or Luigi can defeat Bowser or his duplicates by touching the axe, which cuts the support of the bridge Bowser is standing on and sends him falling into the lava below. When Mario and Luigi do not have the Fire Flower, using the axe is the only way they can defeat Bowser. The use of the axe is seen again in the World-e level Classic World 1-4 in Super Mario Advance 4.
The axe appears in Bowser's court in Mario Hoops 3-on-3, where the basketball hoop's pole is a giant axe. It also appears in Mario & Luigi: Superstar Saga, where it cameos alongside a paper duplicate of Bowser in a Super Mario Bros.-reminiscent section of Bowser's Castle. In New Super Mario Bros., the axe is replaced by a Skull Switch in the game's Bowser battles. In New Super Mario Bros. Wii, a ! Switch is used instead. In New Super Mario Bros. U, the axe serves the same purpose as in Super Mario Bros. Using it will destroy Bowser's bridge and sends him into lava. However, the player doesn't actually utilize the axe directly. Instead, the player has to use a ! Switch to activate it.
The axe appears in Super Mario Maker, as the goal for Castle-style courses. Its appearance is different depending on the game style, but it shares the same function as seen in Super Mario Bros..