"Sonic the Hedgehog" is a 2D side-scrolling platform game. The gameplay centers on Sonic's ability to run at high speed through levels that include springs, slopes, bottomless pits, and vertical loops. The levels are populated with hazards in the form of robots inside which Dr. Robotnik has trapped animals. Destroying a robot frees the creature, but is not necessary to complete the game. The player must also avoid touching spikes, falling into bottomless pits, and being crushed by moving walls or platforms, as well as drowning, which may be prevented by breathing air bubbles from vents. Sonic's main means of attack is the Spin Attack, in which he curls into a ball and rapidly spins his body, damaging enemies and certain obstacles upon collision. This may be performed by jumping or by rolling on the ground.