Fire Bar

Firebars are rotating rods that are formed from fireballs; they are generally found in fortresses. They debuted in Super Mario Bros.. Although not a living enemy, they go swinging around trying to hurt Mario or Luigi. In later games, they were replaced with similar-acting enemies such as Roto-Discs and Ball 'n' Chains.

In Paper Mario, the Firebars reappeared in Koopa Bros. Fortress and Mt. Lavalava; this time they swing sideways. They also swing either clockwise or counter-clockwise, if Mario touches one; he loses some HP. Jumping over one of these Firebars causes it to swing faster. If Mario dodges one 10 times, it will vanish and drop a number of coins.

They were the only enemies of the original Super Mario Bros. to not be featured again in Super Mario Bros. 3. They appear in later Mario games such as Super Mario 64, New Super Mario Bros., Paper Mario: The Thousand-Year Door, Yoshi's Island DS, Mario vs. Donkey Kong 2: March of the Minis, Super Paper Mario, Super Mario Galaxy, and New Super Mario Bros. Wii''. They were also given notable appearances in certain castles of Super Mario World 2: Yoshi's Island, which depicted them as swinging three-dimensionally; a Firebar depicted with eyes working on similar 3D mechanics also appeared in the Bowser Castle of Mario Kart: Double Dash!!.

Super Paper Mario Tattle
"That's a Fire Bar. Don't touch it, or you'll get burned..."

Trivia

 * Firebars were featured as collectible items in Animal Crossing: Wild World and Animal Crossing: City Folk. When it's set down, it plays the Level x-4 theme as the firebar spins on the block.
 * In The Legend Of Zelda: A Link to the Past Firebars spun on the ground.
 * According to Satoru Iwata, "...firebars, which appear in Super Mario Bros., had also been used early on in development of The Legend of Zelda."