Missile Banzai Bill
From the Super Mario Wiki
Missile Banzai Bills are a sub-species of Bullet Bills from New Super Mario Bros. Wii. They act like a Missile Bill, although they are bigger and they do not turn around when they miss a target. They are the same size as a Banzai Bill, and they only appear in World 9-3.
The player can defeat it by simply jumping on its head, or by running into it with a Starman. Also, a Missile Banzai Bill cannot be frozen by an ice ball; it will break the ice and release itself when the ice ball reaches it. Likewise, POW Blocks are useless against them.
On a side note, Missile Banzai Bills are never seen being fired from a Banzai Bill Blaster.