Air bubbles are bubbles of oxygen that allow people to breathe underwater. They usually appear from a crack in the ground and give Sonic the Hedgehog full lungs of air by simply inhaling a fully-sized bubble.
They have appeared on two occasions in Sonic the Comic. The first was a minor appearance, allowing to survive a while longer when battling a whirlpool machine. Noting that Sonic was easily able to survive water-based traps with the bubbles, Doctor Robotnik ordered Grimer to invent something that turned this trick against him. Sure enough, when fighting Badniks in the Aquatic Ruin Zone, Sonic gulped in air but found himself trapped in a tough plastic bubble. Unable to pierce his shrinking cage with a Spiker Badnik, Sonic's only hope was to trick other Badniks to torch the bubble with their fire-breath.