From the Super Mario Wiki
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The Shyper is the strongest variety of Shyster and only appear in Super Mario RPG: Legend of the Seven Stars. Like their Shyster cousins, Shypers are mechanical Shy Guys that ride sword-tipped pogo-sticks. Shypers are one of the strongest enemies in the game, and only appear during the final battle with Smithy. They look identical to Machine Made Shysters.
During the battle between Mario and Smithy, Smelter will produce hot liquid metal from his mouth, which Smithy then shapes with his sledgehammer into Shypers. As such, Smithy has an infinite supply of Shypers at his disposal. Thus, Mario and company should focus their attacks on Smelter, the source of the Shypers, before attacking Smithy.
Not only can Shypers attack Mario with their sword-tipped pogo-sticks, they also possess some of the strongest magical attacks in the game. Their most powerful attack is Sword Rain, which does significant damage to all of Mario's party.