Gumballs[note 1] (ボール,Bōru?, lit. "Ball") are floating round-shaped objects found at Bonus Stages. Each different looking Gumball contains a different item, something else or nothing, that the player mostly or not can picked from monitors as well. Depending on the Bonus Stage, these items are seen floating up or falling down to unknown.
Gumballs are first seen at singular Bonus Stage in Sonic the Hedgehog 3, in which the player needs 50 rings and enter the star circle above a Starpost. Here, Gumballs are inside of large Gumball Machine where the player is able to release them out by rotating the crank on the machine once. Once releasing them, Gumballs start falling down unless the player picks one of them before he/she falls down as well. In Sonic & Knuckles, Gumballs are also collectible items in Glowing Spheres-type of Bonus Stages. If the player touches smaller lighting ball, it will transformed to Gumball, that starts to float up. The player has to touch it again to get the power-up inside the Gumball.
List of Gumball items
Clear Gumball (Clear Ball)
Empty Gumball does not give nothing for the player.
Green Gumballs with REP word on it can replace red springs at the bottom. Due this only works in Gumball Machine-type of Bonus Stages, these variants of Gumballs don't appear in Sonic & Knuckles.
Sonic & Knuckles has unused in-game sprites for two different Gumballs inside the game's code, but which can also be set on by using Debug Mode. The first one is flashing, golden Gumball with S on it, which does nothing but it could be assumed that it could allowed to transform into Super-form once Chaos Emeralds have been collected. The second one is green Gumball with F on it, that also does nothing.
↑Grab extra 1-Ups, bonus power-ups, and Gold Rings by turning the crank of this special Gumball Machine. To find this Bonus Stage, collect 50 or more Gold Rings during a single Act, activate a Starpost and then leap into the tiny stars that appear. - The description about Bonus Stage from the North American instruction manual of Sonic the Hedgehog 3, page 14.