From the Super Mario Wiki
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The spike ball is an ability learned by Bowser in the DS game, Mario & Luigi: Bowser's Inside Story, and its 3DS remake, Mario & Luigi: Bowser's Inside Story + Bowser Jr.'s Journey. The ability is learned at Peach's Castle Garden when Mario and Luigi cure Bowser of his back pain by drilling into the center of the Lumbar Nook. When they finish the process, Bowser's back loosens; he becomes more flexible and can use the spike ball ability. This ability allows Bowser to roll up into his shell to become a spiky ball when the player selects the ability using the shoulder buttons. He can use this ability to climb walls of soft dirt, smash through certain objects, get shot through a spring and activate treadmills in the overworld. During the battle with Super Peach's Castle of Fury, Giant Bowser uses the spike ball to defend against one of its attacks.
When Bowser is burned by the twin fire-breathing Piranha Plants, and when fighting Dark Bowser at Peach's Castle, Mario and Luigi can visit the Chest Station in order to play a minigame where they can fling Bowser while he is in his spike ball form.
A slightly similar ability was utilized by Bowser in Super Mario Galaxy during the last fight against him in the final galaxy of the game, Bowser's Galaxy Reactor. It could be countered by spinning a rubbery bulb at him during the second phase of the fight. In Super Mario Galaxy 2 during the final battle, he would briefly use this ability to move from side to side, during which the meteorites would bounce right off him if ground-pounded at him. During the second Bowser battle in the Moon Kingdom in Super Mario Odyssey, Bowser would occasionally attack Mario by throwing burning Bowser shells similar to the spike ball at him, replacing the brick-like boulders during his first battle in the Cloud Kingdom.
He also uses this move during the first battle against him in Mario & Luigi: Dream Team. First, he blows fire across the path and then curls up to chase Mario. The player must jump over the smaller fire walls and move around the big ones. Eventually, Bowser will trip and the chase will end.