He is the last boss in The Gauntlet.
Punch - Mario and Luigi should jump to avoid a successful punch. They can also counterattack if they land on his fist. If the Bro jumps before Bowser nearly punches him, he will miss.
Fire Breath - Fireballs must be jumped over or hammered by the Bros. When he shoots a fire stream, the Bros must jump onto Starlow into the air or else they'll take lots of damage.
Goomba Storm - Bowser uses his Special Attack. When the Goombas are charging at them, Mario and Luigi have to jump over them to dodge. When some Goombas come down after being thrown into the air by Bowser's fire breath, the Bros can counter them with the hammer.
In the DX version of Mario and Luigi: Bowser's Inside Story the battle remains the same but with some tweaks
Bowser's Inside Story: Do not use your best Special Attacks against him until he's been thoroughly weakened, because whenever you use a Special Attack, he will inhale it, making it unavailable to use for the rest of the battle.
- Bowser X is the only X boss in Mario & Luigi: Bowser's Inside Story to not be recolored but identical to the original Bowser.
- Bowser X has the most HP out of every enemy in the entire game, at over 7000.
- In Dream Team's Battle Ring, rather than having Antasma X forcibly popped out of Bowser X and both subsequently retreating, they instead explode in defeat like all but two other bosses.