Bowser X is a boss that first appears in Mario & Luigi: Bowser's Inside Story. This upgraded form of Bowser only appears in the Challenge Node in Bowser's body and the Battle Ring. To get to him, the player must beat all X bosses without dying, and then face all the other X bosses in a row before facing Bowser X. He is the only X boss without a color change from the original.
Bowser X re-appears as an extra boss in the game Mario & Luigi: Dream Team. As with the previous title, Bowser X is a stronger version of Bowser who appears as an X boss in the Battle Ring in Pi'illo Castle. He is faced twice: once in normal form, and again in giant form. He is the second normal X boss faced, and the final giant boss in the Battle Ring. Once more, he is the only X boss to retain his normal palette.
Mario & Luigi: Bowser's Inside Story
Like all the other X Bosses in the Challenge Node, Bowser X has upgraded stats. He is capable of performing all of the original Bowser's attacks, plus three new ones. However, Bowser X only uses two of his minion attacks (Unless Bowser did not rescue Shy Guy Squad). The attacks Bowser X performs during battle include:
Mario & Luigi: Dream Team
During the first battle against Bowser X, he is accompanied by Antasma X in his bat form. Bowser X uses all the same tactics Bowser does for this battle: He can spew purple waves of fire at Mario before launching a bigger flame attack that Mario must jump over. He can also roll up into his shell and chase Mario through the foreground, creating flames that Mario must avoid while running; the red flames are avoidable by jumping, while the purple ones must be avoided completely. Bowser X will also attempt a sliding punch, which Mario must counter with his hammer; before punching, Bowser X may teleport behind Mario to catch him off guard. Unlike the real world battle where Antasma is forcibly popped out of Bowser and they retreat, Bowser X and Antasma X explode in defeat.