The Koopa Bros. are a team of four Ninjakoopa brothers and minions of Bowser and powerful rivals of Mario. They appear in both Paper Mario and Super Mario Bros. Zas major antagonists. They were first fought in a big Bowser suit, which Mario destroyed easily, and then fought Mario altogether. Eventually, Mario finally defeated them and they fell into their own dungeon. However they return in SMBZ, ordered by Bowser to steal the Chaos Emeralds. They battle Mario, Luigi, Sonic the Hedgehog and Shadow the Hedgehog. While the Heroes gain the upper hand, the Koopa Bros. unknowingly use the Chaos Emerald to power up, making their spinning attack super powerful, knocking out the heroes. They later fight the Heroes and the Axem Rangers X on Yoshi's Island, only to be brutally slammed into by Mecha Sonic, causing them to be knocked out. They presumably die when Yoshi's Island is destroyed.

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