King Bill

King Bills are a variant of Bullet Bill that first appeared in the final level of New Super Mario Bros. Wii, World 9-8. They are grey in color, with a "goofy" grin as opposed to a menacing grin, and are the largest known Bullet Bills in the Mario franchise, dwarfing Banzai Bills.

New Super Mario Bros. Wii
In the game, King Bills are invincible and unable to be beaten with any maneuver or item, and can only be avoided by bouncing above them with clouds or avoiding their paths. Even a Star cannot defeat a King Bill, though it will keep one from harming Mario. The only way a King Bill can be defeated is by jumping on the Goal Pole.

The players are warned about the incoming King Bills in the form of groups of Coins shaped like a bullet, and many stone blocks that cannot be destroyed without the King Bill's assistance. King Bills will also destroy most other blocks in the area, such as the Used Blocks, ? Blocks, and Brick Blocks.

Mario must also avoid going too high to avoid the King Bills. Since the whole level has clouds at the bottom that make Mario bounce very high, he occasionally must try to bounce under the stone blocks to avoid going too high and not hit them. At the end of the level, a King Bill will chase Mario, and he must get under it and reach the end-level flagpole. Like the original Banzai Bills in Super Mario World, their presumed blasters are never seen.

They are very large in size, taking up nearly the entire screen, which makes it much larger than the previous biggest Bill, the Banzai Bill. It is the biggest non-boss enemy of the game. It is also most likely the second-biggest enemy of the game (including bosses), the biggest being the giant Bowser. The King Bill's eyes follow Mario's movements.

There is a total of seven King Bills in New Super Mario Bros. Wii, all of them appearing exclusively in the aforementioned level, World 9-8.

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, but it was later reused in New Super Mario Bros. U.

New Super Mario Bros. U
King Bills reappear in New Super Mario Bros. U, making their only appearance in the level, Flight of the Para-Beetles. Their flight paths are still marked by coins in the shape of Bullet Bills and their pupils still follow the closest player. This time, however, the King Bills are enveloped in yellow flames similar to that of Mad Banzai Bills, and they move at a slower speed. Only five King Bills make an appearance in the aforementioned level. Like in New Super Mario Bros. Wii, King Bills are immune to any attacks, but they can be defeated in Super Boost Mode.

New Super Luigi U
King Bills only appear at 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.

Trivia

 * Erroneously, the Prima Player's Guide for New Super Mario Bros. Wii uses the term "King Bill" as a catch-all for any large Bullet Bill variations rather than a specific enemy, as it was also applied to Banzai Bill and its Mario-seeking variant.
 * However, they were also named "King Bills" in Puzzle & Dragons: Super Mario Bros. Edition, confirming their name.