From the Super Mario Wiki
Octoguys are enemies appearing in the game Super Mario Galaxy and Super Mario Galaxy 2. They resemble red Octoombas with lighter pink spots. They are different from other Octoombas because they can spit rocks upwards and will attempt to run away at times making them harder to defeat, however, they will eventually become tired and they will stop running to catch their breath. This gives Mario an easier attempt to defeat them.
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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