Gumballs are round containers in varying colors and marks on them based on the item or power-up they contain, much like the Monitors. Depending on the Bonus Stage, these objects either float in midair or drop down from above.
In Sonic the Hedgehog 3, gumballs appear inside the giant item machine in the Gumball Machine-type Bonus Stages. Here, the player can release them by rotating the crank on the machine once. Once released, the gumballs will fall down into oblivion unless the player touches them before that happens. In Sonic & Knuckles, gumballs also appear in the Glowing Spheres-type Bonus Stages. If the player touches a small lightning ball in these stages, it will transformed into a gumball that starts floating up. The player has to touch such gumballs again to get the power-up inside of them.
Green gumballs with "REP" on them can replace the red Springs at the bottom. Since this only works in the Gumball Machine-type of Bonus Stages, this gumball variant does not appear in Sonic & Knuckles.
Gumballs (referred to as "item balls" in Japan) may have been based on the plastic capsules meant for dispensing small toys from Japanese automatic vending machines (自動販売機,jidō-hanbaiki?). Furthermore, in the Japanese manual, the description for the "Clear Gumball" says it is “a ball with nothing in it”, indicating that they are item containers. However, a common misconception caused by the localization team at Sega made them rename the objects as "gumballs" as a reference to the chewing gum often dispensed from western gumball machines.
Sonic & Knuckles has unused in-game sprites for two different gumballs inside the game's code, which can be utilized using Debug Mode. The first one is a flashing, golden gumball with an "S" on it. It does nothing, but it could be assumed that it would allow one to enter a Super State once the Chaos Emeralds have been collected. The second one is green gumball with an "F" on it, which also does nothing.