From the Super Mario Wiki
Gu Goombas are enemies found in the game Super Mario RPG: Legend of the Seven Stars. Mario and his party first meet this variation of Goomba in Bowser's Keep. Gu Goombas are just like regular Goombas, except they are much stronger. They are also green instead of brown. Interestingly enough, if Bowser is fighting alongside Mario, Gu Goombas will not attack and instead flee. However, if Bowser is not in the party, the Goombas will become confused and sometimes attack themselves or other monsters. Hyper Goombas from the Paper Mario series greatly resemble Gu Goombas.
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