Air Bubble

Air Bubbles (気泡) are large bubbles filled with oxygen that appear in the Sonic the Hedgehog series. In underwater-themed levels they periodically rise in small clusters from cracks in the floor. These bubbles provide extra air for playable characters to breathe, and they are necessary to survive being underwater for longer periods of time. Without using air bubbles underwater, the playable character will eventually drown, thus causing the player to lose a life.

The Air Bubbles first appeared in Sonic the Hedgehog (1991) and have since appeared in almost every water-themed level in the Sonic the Hedgehog series. While the air bubbles' purpose and functions have remained the same in all games, there have also been cases in several games where they have aided the player in other ways.

Overview
Air bubbles are always found in sections of the Zones that are submerged in water; though, they do not appear in all underwater sections. In these sections, air bubbles can usually be found emerging periodically from the ground in small clusters. In cases such as Carnival Night Zone Act 2 though, air bubbles can also found by popping balloons whilst underwater. Once an air bubble has emerged, it starts rising up to the surface until it reaches it and simply disperses.

When a playable character has to stay underwater for longer periods of time without drowning, the player has to make the playable character make physical contact with an air bubble, before said playable character drowns. This will make the playable character automatically inhale the air bubble and cause it to vanish, thus restoring the playable character's oxygen supply, and extend the time the player can remain underwater. The extended time underwater that air bubbles grant the player is limited though, and the playable character will eventually start to run out of air once more.

While numerous air bubbles of all sizes are always released from their point of origin, it is only the biggest of them that the player can use to restore the playable character's oxygen supply, while the smaller ones go unnoticed by the playable character. As such, the player often has to wait until a large enough air bubble pops out of the ground to be inhaled.

Air bubbles are not necessarily needed by the player when passing through underwater sections, and a player can make it through a Zone without using them at all. However, because some underwater pathways in the Zones can be so long that the playable character cannot make it through them without getting at least one fresh supply of oxygen, air bubbles are usually necessary for the player's survival underwater.

Countdown sequence
In numerous games in the series, including earlier main games for the Sega Genesis, if the player is in an underwater section and does not get an air bubble within eighteen seconds, the countdown sequence will start. A small two-note jingle can be heard between five, ten, and fifteen seconds before this happens. When the countdown sequence begins, the game will display a countdown from five to zero on the screen. If the player does not get an air bubble or get back to the surface before the alarm music ends and counter reaches zero, then a second later, the playable character will drown and the player loses a life.

The alarm jingle, that signifies that the player is about to drown, is believed to be composed by Yukifumi Makino, the sound programmer of Sonic the Hedgehog (1991) and it has since then been used in many later games through the series. The following audio track presents how the alarm music sounds like in both the 16-bit version of the original Sonic the Hedgehog and Sonic the Hedgehog 2:

Other game appearances
Air Bubbles' functionality and their purpose have remained constant throughout the majority of the Sonic the Hedgehog series, but there has been some cases in the games where they have had other functions. In games such as the 8-bit version of Sonic the Hedgehog 2 and Sonic the Hedgehog Triple Trouble, there are larger air bubbles that can surround the player. Whilst inside this type of air bubble, the player cannot drown and will float slowly to the surface, while the player can move left and right as well as changing the speed of ascent by pressing up or down on. The Air Bubble can be popped by Spin Jumping out of it, hitting spikes, hazards and colliding with a wall.

In Sonic the Hedgehog CD, Dr. Eggman is using an underwater vehicle that creates a large shield of Air Bubbles around it in Tidal Tempest. The player is required to inhale the Air Bubbles in order to create an opening, hit, and defeat Eggman. At Water Palace in Sonic Generations, there is a gimmick where player can rotate the wheel to create large air bubbles for the playable character to bounce on to get to the other side of stage.

Air Bubbles appeared in the last chapter of Sonic Chronicles: The Dark Brotherhood when Team Sonic and Tails enter Perfect Charyb's lair of Nocturne. Perfect Charyb appears and floods the lair with water. While moving around the submerged lair, the player's party will gradually lose POW Points (PP). The player can refill their PP using the air bubbles. Once a character's PP reaches zero, that character's HP will then deplete until it reaches one.

Sonic the Comic
In Fleetway's Sonic the Comic, some stories depict Air Bubbles in flooded zones and locations. When getting trapped by debris, Sonic tries to reach Air Bubbles, but he's unable to do so until the giant stone Sentinel rescues him from drowning. One instance, Grimer invented a trap to catch Sonic located within the waters of Labyrinth Zone. Sonic was ambushed by new spider badniks that shot fire, and fell into the water. After fighting a pair of Spiker badniks, he found a vent of Air Bubbles where the trap was located and was engulfed by a impenetrable bubble of ultra-tough plastic. This trap was similar to the larger air bubbles in the 8-bit games, albeit with limited air and without buoyancy. He escaped the trap using the flames of the new spider badniks.

Adventures of Sonic the Hedgehog
On one occasion in Adventures of Sonic the Hedgehog, Doctor Robotnik and his son manage to drop Sonic into the sewer, but he is later seen inhaling Air Bubbles to survive underwater.

Archie Comics
One time in the Archie' Sonic the Hedgehog miniseries, Sonic was about to drown after keeping himself from being pulled into an underwater Roboticizer by Jaws. Fortunately, thanks to a distraction provided by Tails and Rotor in the Bathysphere, Sonic was able to get some air from some Air Bubbles they made, and destroyed the Roboticizer.

Sonic X
In the Sonic X comic series published by Archie Comics, Sonic and Amy used Air Bubbles to breather while Knuckles and Rouge dealt with the surroundings.

Trivia

 * In most of 3D games, the player instantly dies when falling into the water. He/she can, however, run across the water at a certain speed and at right angles.
 * Despite that Sonic Rush Adventure has underwater sections, it does not have any air bubbles.
 * There are certain games in the series, which don't feature the infamous alarm music at all. Many of those games include Master System and Game Gear games, while as it isn't featured in Sonic the Hedgehog CD, where instead eerie bubbling sound starts playing in the background during the countdown. At Water Palace in the Nintendo 3DS version of Sonic Generations, the alarm music isn't featured as well.