Kent C. Koopa
From the Super Mario Wiki
Kent C. blocks Pleasant Path, the road to Koopa Village and the Koopa Bros. Fortress after Chapter 5, preventing Kolorado from getting home after the explorer's adventures on Lavalava Island. He demands a toll of one hundred coins in order to let people pass, but Mario can fight him instead instead as an optional boss. Defeating him will cause him to flee from the path for the rest of the game. Russ T. implies that Kent C. Koopa taught the Koopa Bros. how to fight.
Kent C. Koopa has rather high attack and defense compared to other bosses encountered before and after the point he appears in the game. Kent C. can use a powerful Ground Pound-like attack on Mario to squish him for ten damage; he may also perform a slow Shell Toss attack that flattens Mario and their partner, inflicting the injured status effect on them while dealing three damage.
Unlike other Koopas, Kent C. requires Mario to land two jumps in order to be flipped over, and he will immediately get back up that same turn; also unlinke other Koopas, getting back up does not use up that turn, and he will attack as normal. While flipped, Kent's defense is halved to 3, and his tail can also be targeted and has a defense of 0. Using the Spin Smash attack on Kent C.'s tail while he is flipped over makes him spin around, causing him to drop a few coins. Kent C. is also vulnerable to being put to sleep by moves such as Mamar's Lullaby, and will not get up as quickly he is asleep while flipped.
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