Cannonball

Cannonballs are heavy metal spheres that are launched from cannons. Mario and Luigi are able to stop the lethal shots by stomping on them in mid-air; they can also be dodged relatively easily.

Super Mario Bros. 3
They appear most prominently in Super Mario Bros. 3 where they are fired from cannons mounted on Bowser's tanks, boats, and airships.

Super Mario Galaxy
Cannonballs reappear in Super Mario Galaxy with a renewed appearance. They sport a white line around their center and two yellow circles on opposite sides. In this game, cannonballs are fired by cannons located in Battlerock Galaxy and Dreadnought Galaxy, as well as from airships in Bowser Jr.'s Airship Armada. One notable difference with these cannonballs is that rather than simply colliding with the hero they explode upon impact. This will knock Mario down and may also result in him being thrown off a platform or into a black hole. To attack a cannonball, the player must jump on it or shoot it with a Star Bit. The first three cannonballs originating from the same cannon to be destroyed this way produce a coin each.

New Super Mario Bros. Wii
Cannonballs make another return in New Super Mario Bros. Wii, in which they only appear in World 8's airship. The giant cannonballs also return from Super Mario Bros. 3. Since the cannons are always found in a group, there is a high chance for the player to earn endless 1-Ups by jumping on each cannonball consecutively without touching the ground.

Super Mario Galaxy 2
Cannonballs make a reappearance in Super Mario Galaxy 2, retaining their function from the predecessor, though they only appear in Fleet Glide Galaxy.

New Super Mario Bros. U
Cannonballs also appear in the Wii U title, New Super Mario Bros. U, where they act just like the ones in the predecessors. They can only be found in The Mighty Cannonship, from Soda Jungle. There is also a Challenge called Airship 1-Up Rally, which consists of jumping on many Cannonballs without falling to receive many 1-Ups. Cannonballs do not reappear in New Super Luigi U.

Super Mario 3D World
Cannonballs appear again in Super Mario 3D World, in which they are fired out of cannons and Cannon Boxes.

Super Mario Maker / Super Mario Maker for Nintendo 3DS / Super Mario Maker 2
Cannonballs reappear in Super Mario Maker, Super Mario Maker for Nintendo 3DS, and Super Mario Maker 2, where they come from cannons. Shaking a cannon will make it produce red cannonballs, which are much faster than normal ones. When a Mushroom is dragged onto a cannon, it will shoot Giant Cannonballs.

In the version 3.0.0 update for Super Mario Maker 2 the Cannon Box was added as a power-up.

Super Mario Run
Cannonballs appear in Super Mario Run, behaving similarly to Super Mario Bros. 3. They are found in the levels Airship Cannons...Fire!, Airship Armada, and Secret Course 10.

The Adventures of Super Mario Bros. 3
Cannonballs occasionally appear in several episodes of The Adventures of Super Mario Bros. 3.

Mario is Missing!
In the game Mario is Missing!, Luigi has to return the cannonball of the Emperor's Cannon to the Kremlin. It had been stolen by Koopa Troopas.

Mario & Luigi series
Cannonballs appear again in Mario & Luigi: Superstar Saga, where they are fired at the Mario brothers by Gunner Guys in battle. They reappear in Mario & Luigi: Dream Team as one of the methods of attack for Shy Guy Airtubs, and their stronger relative, the Shy Guy Airtub DX.

Wario World
In Wario World, Captain Skull shoots gigantic, white cannonballs with human-like faces on them, which explode upon impact.

Super Smash Bros. series
Cannonballs are shot by Bowser Jr. in his standard special move in Super Smash Bros. for Nintendo 3DS / Wii U and Super Smash Bros. Ultimate, Clown Cannon.

Paper Mario: Color Splash
Cannonballs appear in Paper Mario: Color Splash, where they are fired from the Violet Passage captain's ship. When Shy Guys take over the ship, they fire the cannonballs randomly, narrowly missing Huey. Mario can use the cannonballs to hit targets and collect coins in the Violet Passage.

Super Mario Run

 * Notebook bio: ''"A projectile fired from a cannon, it travels slowly in the air. Its smooth surface can easily be stepped on."

Trivia

 * In Mario vs. Donkey Kong, Mario will not get struck by a cannonball if he makes contact with one during certain frames of the backflip animation.