Inbetween each stage, a map of South Island displays the location of the next level and the path through it. Sonic begins the game with 3 lives, though more can be earned by collecting 100 Rings in any Act or amassing a total score of 50,000 points. (Continues, each worth a full set of 3 lives, can be procured from Item Boxes in the Special Stage.) Each remaining life is worth 5,000 points at the final score tally.

   Sonic's Mega Drive moves are all present and accounted for, minus his ability to push blocks:

	walk -- Push left or right on the D-pad to initiate Sonic's movement in either direction. As you hold the button down, Sonic gains speed.
	run -- Begin walking and hold down the button to make Sonic gain speed. After a few seconds, he'll break into a run.
	screech -- While running, quickly press and hold the opposite direction on the D-pad to make Sonic screech to a halt. He'll skid for a short distance, based on how fast he was moving.
	look up -- While standing still, press up on the D-pad to make Sonic gaze to the heavens. As you hold up, the camera pans upward, giving you a view of Sonic's overhead surroundings.
	crouch -- While standing still, press down on the D-pad to make Sonic sniff his crotch. As you hold down, the camera pans downward, giving you a view of the stage beneath where Sonic stands.
	spin (回転) -- While moving, press down on the D-pad to make Sonic curl into a rolling attack. He'll remain in this position until you jump or slow down. The speed of Sonic's movement while in spin form is based on how fast you're moving when you launch it, and also on the terrain Sonic rolls along.
	spin jump (回転ジャンプ) -- Press 1 or 2 at any time to make Sonic leap into the air with a spin attack. The height of the jump is proportional to how long you hold the button down.

   Most of the basic items from the Mega Drive version have made the cut:

	Ring (リング) -- As long as Sonic has some of these, he won't lose a life if he takes damage. You get an extra life for every 100 you collect, but the count is reset to 0 in exchange. Each Ring on hand is worth 100 points at the end-of-Act score tally. (Note that Sonic cannot retrieve lost Rings.)
	Item Box (アイテムボックス) -- In each stage, you'll find a number of these power-up bearing monitors. Pop them open with a spin to procure one of six power-ups along with a 100 point bonus at the end-of-Act tally: Big 10 Ring (ビッグ10リング) - Worth 10 Rings Barrier (バリア) - Absorbs one hit High Speed (ハイスピード) - Temporary speed increase Muteki (無敵) - Temporary invincibility 1up - Gives Sonic an extra chance Point Marker - (ポイントマーカー) - You return to this point if you lose a life.
	spring -- Leap onto the broad side to catapult Sonic into the air.
	spikes -- Don't touch the pointy side, stupid.
	switch -- Jump on the button to cause a change in the nearby scenery, usually necessary to proceed.
	air bubbles -- Large, oxygen-filled bubbles periodically rise from these clusters: tag one to fill Sonic's lungs with air and prolong the time you can spend underwater.
	Chaos Emerald (カオスエメラルド) -- Chaos Emeralds are not to be found in Special Stages this time but are hidden in the nooks and crannies of action stages. There's 1 in each Zone for a total of 6 (all the same color). Each Emerald is worth 20,000 points at the end of the game score tally.
	Bonus Plate (ボーナスプレート) -- These signs can be found at the end of each first and second Act. Cross them to end the stage. You get a bonus depending on what's on the sign's face when it stops spinning: Eggman (nothing), Ring (worth 10 Rings) or Sonic (1up). If you have 50 Rings on hand when you cross the Bonus Plate, you'll spin an exclamation point and warp to the Special Stage.
	capsule -- These are found at the end of each third Act, after defeating the boss. Push the button on top to destroy the machine and free the helpless animals within.

   Most of the baddies present in the Mega Drive version have found their way into 8-bit land, though they seem to have lost maneuverability in the process. Fuzzy animals running free would require too much processing power, so now when you bop a bot all you get is a poof of smoke and a tinny 8-bit sound effect. Each busted bot is worth 100 points at the end-of-Act score tally.

	Motora (モトラ) -- Beetle bots that roll innocently along the ground.
	Gani-gani (ガニガニ) -- Crab bots that crawl along the ground and fire projectiles from their pincers. ("Kani" is Japanese for crab.)
	Beeton (ビートン) -- Bee bots that fly across from the right side of the screen, pausing once to fire a large flashing projectile downward.
	Bata-bata (バタバタ) -- Piranha bots that leap upward from beneath bridges. ("Bata-bata" is Japanese for a clattering noise.)
	Yadorin (ヤドリン) -- Hermit crab bots that crawl along the ground. Their shells are cloaked with spikes, making them invulnerable from above. ("Yadokari" is Japanese for hermit crab.)
	Meleon (メレオン) -- These chameleon bots hang out on the side of cliffs and remain invisible until approached, then appear just long enough to fire an energy blast at Sonic.
	Mogurin (モグリン) -- Mole bots that roll back and forth along the ground, then leap like lunatics as soon as Sonic approaches. ("Mogura" is Japanese for mole while "moguri" means diver.)
	Puku-puku (プクプク) -- Piranha bots that swim around underwater. ("Puku-puku" is Japanese onomatopoeia for a bubbling noise.)
	Unidus (ウニダス) -- Irritable sphere bots that hover around very slowly. They're orbited by 4 spiked balls which they fling off in rapid succession upon being approached. It's a dangerous assault, but once it's done, Unidus is completely open to attack. ("Uni" is Japanese for sea urchin.)
	Nal (ナール) -- Caterpillar bots that crawl slowly along the ground. The safest method of disposal is to roll into their spherical noggins: venture a poke anywhere else and you'll sustain damage and send their segments flying.
	Ton-ton (トントン) -- Pig bots that hop in place atop steep banks and roll balls down the slope. ("Ton" is a prefix used to identify several Japanese pork dishes.)
	Uni-uni (ウニウニ) -- These guys, palette aside, look exactly like Unidus. They're a bit more cool-headed, though, and won't fire off their barrier of orbs. While this means you don't have that tricky attack to avoid, they're virtually impossible to hit.
	Bomb (ボム) -- Mindless kamikaze bots that waddle along the ground or ceiling and explode into a shower of projectiles when approached. They can't be damaged, only avoided.

   There are six stages to clear, three of which have been reproduced from the Mega Drive version and three of which are original. Each stage consists of two areas and the boss round. Bosses take eight spins each, but it should be noted that every boss in the game must be fought without the luxury of a single Ring. So don't miss.

Green Hill -- Act 1 is visually similar to the original 16-bit version, but significantly more straightforward. Act 2 takes place almost entirely in an underground cavern - the Chaos Emerald can be found at the center of the cave at the top of a waterfall. Boss: Eggman hovers around at the top of the screen, occasionally dropping down to make a dash attack. Only during this attack does he put himself within spinning range.

Bridge -- The checkered hillsides are replaced with diamond mesh on this mountain lake. Use the teeter-totters to spring to higher ground, and keep moving along crumbling bridges. In Act 2, the screen scrolls forward automatically: keep up, but leave yourself enough space to see what's coming. The Chaos Emerald can be found near the end of Act 1, but you'll need sharp timing to retrieve it, as it can only be reached by deliberately falling through a crumbling bridge. Boss: Eggman pops his bald noggin up from the waves, pausing just long enough to fire a trio of flashing projectiles at our hapless hedgehog hero. Ducking on the middle platform will keep you out of harm's way.

Jungle -- Long vines act as platforms and ramps in this lush jungle. Sonic can roll along the surface of the water on logs, but take damage and he'll go for a swim. Act 2 is laid out vertically, and don't look down because if you fall, you lose a life. The Chaos Emerald can be found about halfway through Act 1, near the bottom of a large waterfall. Boss: The arena is a simple bowl-shaped vine. Eggman moves around overhead, occasionally dropping a ball down into the bowl. The ball rolls back and forth a couple of times before exploding, but the good doc has an endless supply.

Labyrinth -- As with the 16-bit stage of the same name, you've got the added task of keeping Sonic's lungs filled with oxygen while underwater. The Chaos Emerald is located at the end of Act 2, trickily placed at the bottom of a set of spikes. The only way to grab it is to make use of the Muteki Item Box hidden a short distance away, then make sure you reach the spikes before the invincibility wears off. Boss: Eggman keeps just out of sight in this arena, but occasionally pops out of one of the 5 openings: 1 of the left, 1 on the right, 2 on the ceiling, and 1 on the floor. As soon as he shows his ugly noggin, he'll launch a hopelessly inaccurate homing missile. When he pops up from below, he fires a couple of flashing projectiles. He can only be damaged when he's launching his attack.

Scrap Brain -- It looks like the same stage you played on Mega Drive, but the layout is far more labyrinthine than your previous outing through the Zone. Like the first time, though, Scrap Brain has no boss. The Chaos Emerald can be found midway through Act 2: when you come to a fork in the road, take the upper path and navigate a maze of teleports.

Sky Base -- Eggman takes to the skies in the unlikely debut of another Sonic tradition: the flying fortress. Act 1 features a web of electrical conduits in the background... they're harmless until they light up, which they do periodically. Act 2 is a mess of big-ass guns, and not a Ring in sight. The final Chaos Emerald is located near the end of Act 2, but in order to reach it you need to take a shortcut at the beginning of the stage that leads to a series of dangerous leaps. Boss: The final boss arena is swept by an electric laser while Eggman cowers in a glass tube on the right side of the screen. Every once in a while he'll jump in the air and push a button that causes a spark to fly out of the glowing orb on the ceiling.

   Cross a Bonus Plate with at least 50 Rings and you'll spin an exclamation point which will send Sonic into the Special Stage. The Special Stages aren't for Chaos Emeralds this time, they're just a diversion. Sonic runs around a pinball arena filled with Rings, springs, bobbins, and Continue Item Boxes. Springs come in three different colors, each packing a different punch: purple (low), orange (medium), and green (high). Run around grabbing all the loot you can, but make sure to hit the exit before the 2-minute timer runs out or you won't get to keep any of the spoils. There are 3 Special Stage layouts with two variations a piece: in the variant set, item placement is trickier and time limits are halved.

Can't... breathe... *gasp*	The narrower screen can present a problem at high speeds, hence these new "warning" signs.
You can now attack the Green Hill boss while he's hovering overhead, making this the easiest boss in Sonic history.	The Bridge Zone boss now actually includes bridges.
You no longer die if you fall along the vertical ascent through Jungle Act 2, making the experience as a whole alot less traumatic.	Level design in the Labyrinth Zone is almost entirely different. The Chaos Emerald can now be found lying in the wide open near the end of Act 2.
The electric wall at the final boss is replaced by a trio of flame-spouting floor tiles. The spark gun is now in the middle of the screen, making it more difficult to avoid.	The Special Stage level design is completely different.

   In 2003, Sega of America introduced its mobile line under the Sega Mobile label. One of the first games released was a port of the Game Gear version of Sonic 1, compatible with Palm Tungsten C, Tungsten T, and Zire 71. I haven't had the opportunity to play the mobile version, but I assume it's a direct port.