The evil Dr. Robotnik is back, and this time in a portable format. Sonic the Hedgehog for the Game Gear is a portable adaptation of the Genesis side-scrolling platform series starring Sega's hedgehog mascot. As in the 16-bit original, Sonic must find and defeat Dr. Robotnik so that he can free his animal friends.  Sonic can run, jump, or roll his way through stages. While jumping, Sonic curls up into a ball and can attack the various robotic creatures; alternatively blasting on the ground with a curled up and rolling Sonic can also dispatch enemies. If enemies touch Sonic while he isn't curled up, they can damage him. Sonic can find and collect gold rings, however, which allows him to survive the touch -- but at the cost of losing all his rings. Without any rings, Sonic dies when enemies attack him.  Players must guide Sonic through stages filled with hazards like moving or collapsing platforms, spikes, water, or giant springs. To help him in his quest to defeat the evil Dr. Robotnik, Sonic can find and collect a variety of items. Besides acting as an insurance policy against death, gold rings can earn players extra lives (100 rings) or allow them to advance to bonus stages (having at least 50 rings at the end of the level). There are also other items like shields that absorb one hit, temporary invincibility power-ups, red sneakers for extra speed, or even bonus Sonics!