From the Super Mario Wiki
The Armored Harriers are ranked 10th in Glitzville's Glitz Pit. They harbor a huge grudge against Mario after Grubba tells them some rather nasty trash talks that he accredits to Mario (namely the reference to outies running in the family, since their mother apparently had an outie). The Armored Harriers are made of iron that Mario can't break through. He is only able to defeat these two Iron Clefts with the help of Yoshi, who is able to take an enemy into his mouth with his tongue and spit them back at the other enemy. One of them wears red shoes, while the other wears green shoes, implying that the former is older. This type of red and green symbolism appears often in the Mario franchise.
After Mario and his allies beat the Armored Harriers, the two warriors are downgraded to the Minor League. They form a grudge against Mario and attempt revenge by ambushing the plumber after he duels the Tiny Spinies. Although weakened and surprised, Mario defeats the Armored Harriers a second time.
When Mario has to visit the Minor League locker room while searching for the Dubious Paper, the Armored Harriers become very upset.
Despite the twins' grudge against Mario, they, along with Jolene, KP Pete, Rawk Hawk, and a few others cheer him on in his battle against the Shadow Queen. It seems though that they let the grudge go, realizing Grubba lied, but still see Mario as a rival.
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