King Bill

King Bills are variants of Bullet Bills that first appear in New Super Mario Bros. Wii. They are gray with a jovial grin as opposed to other mouthed Bullet Bills' menacing grins and are the largest known Bullet Bills in the Mario franchise, dwarfing the second largest Bullet Bills, Banzai Bills, which they are at least three, if not four, times the size of. They take up nearly the entirety of the screen's vertical space even after it has been zoomed out to accommodate them. Despite their size, they are relatively short lengthwise, similar to the original sprites of both Bullet Bills and Banzai Bills. Unlike the rest of the varieties of Bullet Bills, King Bills do not have their respective blaster shown onscreen, meaning that they are always fired from offscreen areas. When the King Bill spawns, players can see the King Bill's eyes following their character's movements.

New Super Mario Bros. Wii
There are a total of seven King Bills in New Super Mario Bros. Wii, all of them appearing exclusively in World 9-8. In the game, King Bills are invincible and unable to be beaten with any maneuver or item, including Stars, and can be avoided only by bouncing above them with clouds or avoiding their paths. The only way a King Bill can be defeated is by jumping on the flagpole. Landing on a King Bill will cause the player to take damage.

Incoming King Bills are signaled in the form of coins shaped like a bullet. They are also used to destroy stone blocks that wall off sections of the level. King Bills can also destroy most other blocks in the area, such as Empty Blocks, ? Blocks, and Brick Blocks. At the end of the level, a King Bill chases Mario, and he must get under it and reach the end-level flagpole.

Unused animation files found within New Super Mario Bros. Wii suggest King Bills were originally going to be able to be defeated by another method, though it was later reused in New Super Mario Bros. U.

New Super Mario Bros. U / New Super Mario Bros. U Deluxe
King Bills reappear in New Super Mario Bros. U and its port, making their only appearance in the level Flight of the Para-Beetles; only five King Bills appear in that level. They work like they did in New Super Mario Bros. Wii, and are signaled in the same way. This time, however, the King Bills are enveloped in yellow flames similar to that of Mad Banzai Bills, they move at a slower speed, and they can be defeated using the Boost Star in Boost Mode.

New Super Luigi U
King Bills appear only in two levels in New Super Luigi U. They first appear at Larry's Trigger-Happy Castle, chasing after the players as they head to the boss door. Their second appearance is at Para-Beetle Parade. Compared to in New Super Mario Bros. U, the King Bills in New Super Luigi U move at a faster speed.

Puzzle & Dragons: Super Mario Bros. Edition
King Bills make an appearance in the game, Puzzle & Dragons: Super Mario Bros. Edition, serving as one of the various enemies that the player can come across. Its main attribute is Dark, while its sub-attribute is Fire.

The King Bill's skill can lower the defense of all enemies to 0 for one turn. Its Awoken Skill raises the ATK of the player's team members.

When fought as an enemy, the King Bill always starts off by delivering a first strike attack. It then attacks every two turns. When the King Bill does make a move, it might increase its ATK before attacking the player.

The King Bill's greatest stat is its ATK, while it has average HP, and an abysmal RCV.

The player can transform a Banzai Bill into a King Bill by giving it 6 Fire Flowers.

New Super Mario Bros. Wii
Card Number: 39 (Normal), F21 (Silver)
 * Trading Card description: "Here comes king-sized destruction. King Bills are gigantic bullets that come flying across the screen destroying everything in their paths. They are totally invincible to any weapons or maneuvers used against them. The best plan is to stay out of their path. Star power will help keep Mario protected in case of a run in but it won't hurt King Bill."

Trivia

 * The Prima Games guide for New Super Mario Bros. Wii uses the term "King Bill" as a catch-all for any large Bullet Bill variations, as in addition to this specific enemy, it was also applied to Banzai Bill and its homing variant . This is not the case in later appearances.
 * A massive Banzai Bill found in leaked data for Super Mario World on July 24, 2020 would've predated the King Bill had it been incorporated in the final game.