Missile Banzai Bill
From the Super Mario Wiki
Missile Banzai Bills are a sub-species of Bullet Bills and Banzai Bills from New Super Mario Bros. Wii. Unlike Missile Bill, they only have a limited homing ability where they will track their target's vertical position and then continue forward once they reach that height. Their animation is very limited as well, always maintaining a horizontal position and never turning to point at their 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.