From the Super Mario Wiki, the Mario encyclopedia
Barrel Volcano is a volcano that Mario, Mallow, Geno, Bowser and Princess Toadstool enter to find the sixth Star Piece in Super Mario RPG: Legend of the Seven Stars. Mario reaches the Barrel Volcano by jumping right into the crater from the clouds of Nimbus Land.
The Star Piece is guarded by the Czar Dragon, but after they defeat it and get the star, it is stolen by the Axem Rangers. Mario and his party chase the Axem Rangers through the volcano and end up on top of it, where the Axem Rangers get onto their huge battleship Blade, but are followed by Mario. Mario battles the Axem Rangers on Blade, defeats them and destroys the ship.
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