King Bill

King Bills are a new sub-species of Bullet Bill that have so far only appeared in the last level of New Super Mario Bros. Wii; World 9-8. King Bills are invincible, being unable to be beaten through any maneuver or item, and can only be avoided by outrunning and reaching the end-level flagpole. Like Banzai Bills in Super Mario World, King Bill Blasters are not seen.

It's very large in size, taking up nearly the entire screen, which makes it much larger than the previous biggest Bill, Banzai Bill. It is the biggest non-boss enemy of the game, being beaten out by Bowser's giant form after Kamek's spell in Bowser's Castle.

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

On a side note, the player is warned about the incoming King Bills in the form of Coins that make a Bullet Bill shape design and several stone blocks that cannot be destroyed by anything except them.

There are a total of 7 King Bills in New Super Mario Bros. Wii.

Trivia

 * The Prima Player's Guide for New Super Mario Bros. Wii erroneously referred to the Banzai Bill as a King Bill.