From the Super Mario Wiki
Choppahs are a type of enemy appearing in the game Super Mario Galaxy 2. They appear as green creatures that lack legs. They have orange spiked helmets and have a propeller around them, giving them the ability to fly. They fly in a vertical straight line in most galaxies.
They first appear in the Honeybloom Galaxy as the main obstacles. These enemies later appeared in the Sweet Mystery Galaxy, where they were only seen flying horizontally, Honeyhop Galaxy and Flip-Out Galaxy, as well as during the Grandmaster Galaxy's mission "The Perfect Run". These enemies can only be defeated by being eaten by Yoshi. Most of the time, they appear when the player tries to go through a 2D pathway, but they are less common when the pathway is 3D and mostly the platforms are narrow or have lesser grounds.
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