From the Super Mario Wiki
Octoguys also known as Octoomba Leaders are recurring enemies in the Mario Series. They are in the game Super Mario Galaxy and Super Mario Galaxy 2. They look like regular Octoombas. They are just like Octoombas in Super Mario Galaxy 2 because they can spit rocks upwards. But the main difference between them is that, Octoguys shoot rocks faster, and can chase Mario. Like most enemies, Octoguys can be killed with jumps or spins. Octoguys will additionally attempt to run away from Mario and dodge his jumps and his other attacks by simply backing away from him making them slightly more difficult than Octoombas or Elite Octoombas. They can also cause a distraction against other enemies for the player. However an Octoguy will eventually become tired and will stop running to catch its breath. This gives Mario an easier attempt to defeat them though this means that the player has less than two seconds to react as Octoguys will retain to run away. Humorously if Mario Ground Pounded an Octoguy, it will be flat as a pancake. This can be quite hard though if the Octoguy is running away from Mario. The Octoguy is the most threatening out of all the Octoombas: their shooting is 50% more accurate, they have good distances and can be quite frustrating when fought in large groups. There are two ways to defeat them the easily: the first is that if Mario can't jump on them, he can simply wait until the Octoguy becomes tired. This is Mario's chance to kill them. The other reason is to shoot a Star Bit to make them dizzy. When it is stunned, Mario can then kick it.
Super Mario Galaxy
In Super Mario Galaxy, they are semi-common enemies appearing in mass numbers in the Honeyhive Galaxy, Buoy Base Galaxy, Gold Leaf Galaxy, and Deep Dark Galaxy. In the Honeyhive Galaxy, they appear in the water-filled planet, trying to prevent Bee Mario from getting to the Queen Bee. They also appear on the Queen Bee's planet. Two of them appear on the fortress in the Buoy Base Galaxy. In the Gold Leaf Galaxy, they appear in the final planet of the second mission in the water-filled section. In the Deep Dark Galaxy, they guard a Fire Flower that is needed for Mario or Luigi to proceed through the level. A lone Octoguy also appears in "Bubble Blastoff", trying to knock Mario off a pole he is climbing.
Super Mario Galaxy 2
In Super Mario Galaxy 2, Octoguys return. They appear in the Boulder Bowl Galaxy, in the Honeyhop Galaxy and Shiverburn Galaxy's Prankster Comet mission.
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