Sonic The Hedgehog 2 (World) ROM

Super Speed! Sonic's back and better than ever. He's a blur in blue! A blaze of action! With his new Super Spin Dash. And a new, fabulous friend, "Tails" the Fox. You won't believe it 'til you see it. And when you play, you won't stop. Super Play! Defy gravity in hair-raising loop-de-loops. Grab Power Sneakers and race like lightning through the mazes. All at break-neck speed! Super Power! Sonic's attitude is can-do. The mad scientist Dr. Robotnik is planning a world takeover. Sonic gets tough in the fight to save his friends and squash Robotnik for good!

Some Sega Genesis/Megadrive games saw the light on their lower spec conterparts, the Master System and the Game Gear.
However, in Sonic 2's case there was no direct port, but a unique and awesome experience, with low end graphics and music, but great gameplay.
The story of this one installment is not quite the same as its 16-bit counterpart. Dr. Robotnik (Eggman in Japan) has captured Sonic's sidekick Tails, all while trying to dominate the world too, so Sonic runs towards South Island to rescue Tails and foil Robotnik's plans once again.
As with the previous installment, the Chaos Emeralds are sparsed in the map, hidden in hard to reach spots. Get them all, finish Robotnik's contraptions and then you conquered Sonic 2 for the Game Gear.
The difference between this game and the Master System release is the screen resolution and the coloring. As the Game Gear's screen was capable of more colors, this made the game look really good on this handheld.