King Bill

King Bills are a sub-species of Bullet Bill that have first appeared in the final level of New Super Mario Bros. Wii, World 9-8.

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 neutralize a King Bill, but it can keep one from harming Mario. The only way a King Bill can be neutralized is by jumping on the end-level flagpole, which is proven by the fact that one chases Mario at the end of level 9-8.

The players are warned about the incoming King Bills in the form of Coins that make a Bullet Bill shape design, and many stone blocks that cannot be destroyed by anything except the King Bill itself. The players must make sure that they aren't standing on any such blocks during such a violent destruction. King Bills will also destroy any other blocks in the area. Strangely, The King Bill Warning (coins shaped like a bullet surrounded by blocks) is smaller than the King Bill itself.

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 Banzai Bills in Super Mario World, King Bill Blasters are not seen on screen.

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), first-biggest being Giant Bowser.

They show their teeth, like a Banzai Bill, but in a less menacing way. Additionally, their eyes are less menacing as well. Interestingly enough, the King Bill's eye pupils actually follow Mario's movements.

There is a total of 7 King Bills in New Super Mario Bros. Wii, all of them appearing exclusively in the aforementioned level: 9-8.

New Super Mario Bros. U
King Bills reappear in New Super Mario Bros. U at 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 though, the King Bills are enveloped in yellow light, and they move at a slower speed.

Trivia

 * The Prima Player's Guide for New Super Mario Bros. Wii erroneously referred to the Banzai Bill as a King Bill.
 * Unlike other Bullet Bills, the King Bill smiles; Banzai Bills show an angry expression, while normal Bullet Bills have no mouths at all (with the exception of the ones that appear in Super Mario Sunshine). Also, like the Banzai Bills, King Bills lack arms; a trait that normal Bullet Bills have.
 * Oddly, the King Bill looks almost exactly like the original Banzai Bills from Super Mario World, in terms of its shape.
 * King Bills in the beta version of New Super Mario Bros. Wii were able to be defeated.