From the Super Mario Wiki, the Mario encyclopedia
Superball Flowers, also called flowers or super flower, are power-up flowers that were first introduced in Super Mario Land and reappear in Super Mario Maker 2 30 years later, holding the longest gap between appearances of a power-up in the Mario franchise. Superball Flowers turn Mario into his Superball form, giving him the ability to shoot Superballs.
Super Mario Land
Superball Flowers are very similar to Fire Flowers in appearance and in abilities granted. Superballs are Super Mario Land's equivalent to fireballs; only one can be fired at a time, though, and they bounce diagonally at 90° angles. Superballs will collect any coins they make contact with. While one fireball can typically defeat any non-boss enemy, many enemies require multiple superballs to defeat. Superball Mario looks identical to Super Mario, and can only be found in levels if Mario is Super Mario or won in the Bonus Game.
Super Mario Maker 2
In Super Mario Maker 2, the character who picks them up takes on monochromatic shades of green, and the background music will also change to Birabuto Kingdom's ground theme. The power-up is only available in the Super Mario Bros. game style as an alternate form of the Fire Flower and retains its properties from Super Mario Land. Superballs can also now light Bob-ombs, collect Keys and Pink Coins, and activate P Switches and POW Blocks. Superball Flowers are unlocked by hitting a ? Block that is initially covered by Hard Blocks; by clearing the job Spiny Shell Smashers, given to Mario by Purple Toad, the blocks will be removed, allowing Mario access.
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