Fire Breath is a move Bowser can execute in various games. He will emit fire out of his mouth and burn anyone near. It is Bowser's signature attack.
Super Mario series
Super Mario Bros.
Bowser first uses Fire Breath in Super Mario Bros., as well as throw hammers, along with his impostors. They use it through the level to burn Mario. In the battle, they use it to hinder Mario's progress in crossing the bridge, grabbing an axe to close the bridge, and keep him from rescueing the Mushroom Retainer.
Super Mario Bros. 3
Super Mario World
Bowser uses Fire Breath in Super Mario World. When Mario or Luigi throws Mechakoopas at him, he flies out of control and flies aways and spits flames down at Mario or Luigi. He also does this a second time when they throw Mechakoopas at him again.
Super Smash Bros. series
Fire Breath is one of Bowser's special moves in Super Smash Bros. Melee, Super Smash Bros. Brawl, and Super Smash Bros. for Nintendo 3DS / Wii U. Bowser uses this move when the Button is pressed. It is exactly the same as a Fire Flower, except that the flames get smaller the more it is used. The attack is somewhat of a long-distance move, and is usually best to use when the enemy is coming in for close-range combat. However, the move will leave Bowser motionless while using the attack, and will leave his back open for attack.
In Super Smash Bros. for Nintendo 3DS / Wii U, two variations on the move are introduced: Fire Shot and Fire Roar. Fire Shot releases a singular fireball that takes longer to release, but pierces enemies and is stronger, and Fire Roar loses its range much more quickly and takes longer to recharge, but it is overall stronger and has a much longer reach.
Super Paper Mario
Bowser uses this move in Super Paper Mario and it is his special move in the game. It can be used to light candles. Also it can attack enemies from a distance, giving Bowser a slight advantage.
Mario Power Tennis
In Mario Power Tennis the Fire Breath is the Offensive Power Shot used by Bowser. It involves Bowser breathing fire on the ball and sending it over the court alight. A similar move was seen as Bowser's special shot in the Dream Table Tennis event in Mario & Sonic at the Olympic Games.
New Super Mario Bros. U
Bowser's Fire Breath (referred to in the Prima Games guide as Bowser's Flames) reappers in New Super Mario Bros. U, though it acts more similarly to the raining molten rocks from previous games than his normal fire. On two stages of Peach Castle, Meteor Moat and Firefall Cliffs, the flames rain down from the sky, destroying any Brick Blocks they come into contact with. Bowser is also seen using the move in The Final Battle. These obstacles also appear in the challenge, Cloudy with a Chance of Fire.
Mario & Luigi: Bowser's Inside Story
Fire Breath is also one of Bowser's commands in Mario & Luigi: Bowser's Inside Story. When used in battle, Bowser will inhale and when his face turns red, the player must press and hold or to execute the technique, burning any enemy in his path. The attack can also be used out of battle by pressing to ignite Launch Fits, burn trees and flowers, and more. However, when Bowser first appears in Cavi Cape, he is unable to use this ability due to (as later found out in Plack Beach) a Scutlet clogging his Flame Pipe. Once the Mario Bros. defeat the Scutlet, Bowser's Flame Pipe returns back to normal and he can breathe his fire again.
Mario Golf: World Tour
In Mario Golf: World Tour, Bowser uses this attack on the screen in one of his post-hole animations.