From the Super Mario Wiki
Jack O'Goombas, originally referred to as Pumpkinhead Goombas, are pumpkin-wearing Goombas found in Super Mario Galaxy and its sequel, Super Mario Galaxy 2. Their name and appearance are derived from jack-o'-lanterns.
Super Mario Galaxy
Pumpkinhead Goombas made their debut in Super Mario Galaxy. They can be found in Ghostly Galaxy. These pumpkin-wearing Goombas are capable of producing small blue flames in an attempt to burn Mario, yet the ability is lost when their pumpkin is destroyed. To break their jack-o'-lantern helmets, Mario must spin. Ground Pounding them, however, will destroy both the pumpkin helmet and the Goomba in one pound. Once they lose their Pumpkin cover, they are simply a regular Goomba. If the player Ground Pounds a Pumpkinhead Goomba after it just produced a blue flame, Mario will get burned if he touches it. Also, if one tries to jump on one, the pumpkin won't break. If Mario runs into a Pumpkinhead Goomba as Rainbow Mario, only the pumpkin will break.
Super Mario Galaxy 2
The Jack O'Goombas later reappear in the sequel, Super Mario Galaxy 2. They have not changed much from the predecessor, still wearing a pumpkin mask, releasing blue flames once in a while. These enemies are not limited to haunted galaxies, being found in such places as the Clockwork Ruins Galaxy.
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