This is the introductory stage of the game, and if it seems familiar, that's because it was the very first act of the very first game in the Sonic series. Take some time to get familiar with the game's mechanics and obstacles, as it will only ramp up in difficulty from here. This walkthrough will assume the player character to be Sonic, as his abilities are most limited. Feel free to use the power of flight and feats of strength in order to discover the game's secrets in your own way.
Act 1[edit]
Atop the first hill you come across is a Super Ring Item Box, which should give you a good start as far as ring collection goes. In the leaves of the first tree past the bridge (under which a Chopper Badnik rises and falls) is an Invincibility Item Box. Use it to cross the next bridge and get past some Buzz Bombers with complete immunity. The first spring leads to a crumbling platform, which you can ignore in favor of dropping down to the ground below. This will set you on the path of the giant ring, which if all goes well should lead to your first Special Stage. Jump over some spikes and a spring to reach three more Item Boxes (two Super Ring and one Hyper Ring). Past these is a Moto Bug, which can be rolled into; be careful not to jump too high, as doing so may land you on the ground above.
Remaining on lower ground, jump over the spikes and down the cliff. Make sure to slow down on the crumbling ground below in order to drop down even lower. After hopping off a spring, come to a halt; this spring will attempt to send you back down a hill (to the left), but the giant ring is up over the hill (to the right). Jump onto the top of the loop-de-loop and from here, into a hidden passage in the wall to the right. Enter the giant ring to attempt the first Special Stage; if you don't obtain the Chaos Emerald, there will be many other opportunities. Following the Special Stage, Spin Dash through the breakable wall and beware the Moto Bug and Crabmeat below. Bounce off the spring and continue forward. Jump over the next spring and bounce off the one after to be taken to an area in which rising platforms are surrounded by spikes.
Tread carefully over the platforms, jumping over gaps to avoid the spikes, and deal with some Crabmeats that follow. Past a crumbling platform, run into what appears to be a dead end; this is the location of the second giant ring. After the Special Stage, drop down off the crumbling ground and into a tunnel. This should send you to a spring beneath another crumbling platform (you can backtrack a bit here for an Invincibility Item Box before continuing, as the boss is coming up soon). Up on higher ground is the Star Post, which can send you into a Bonus Stage. Use a spring to get onto even higher ground. Walk a bit further here to encounter the first boss of the game.
The boss is pretty basic: two spheres are chained together, with one hanging off the other. The hanging sphere will swing around in an attempt to collide with the player character, and both spheres occasionally glow red to indicate that hitting them will cause damage. Hit either sphere when they aren't glowing to cause damage to the boss. When one sphere is lost, the other will bounce around the screen on its own. Follow the same pattern in order to beat the boss and gain access to the Signpost (which will fall in the exact position where the boss has been defeated). Keep the Signpost airborne until it falls in front of the sunflower to the right and between the two purple flowers to the left; in both cases, the Signpost will bounce and reveal a hidden Item Box, unlocking the "That's a Two-fer" achievement/trophy.
Act 2[edit]
Take the zipline to a Super Ring Item Box. Up a hill is a spring that will take you up to a new area through some breakable ground. Head left, jumping over some spikes, to find an Extra Life Item Box. There is also an Invincibility Item Box in a tree here. Use the spring to ascend to higher ground and use another spring to ascend even further. A third spring takes you across a gap and a floating platform takes you across another gap, after which you can drop down onto a bridge. A Star Post is a short distance from here; use the hill behind it to reach some floating platforms, which you can in turn use to reach a spring. You should see a giant ring within the wall here, but you can't reach it just yet.
Upon spotting the giant ring, take the spring up to a Star Post. When the ground crumbles, drop down with it instead of taking the zipline. If Sonic has the Lightning Shield (or Tails accompanying him), he can jump up from the loop-de-loop to a platform to the left that leads into the giant ring. Back on the loop-de-loop, drop down and continue forward. After jumping over some springs, you should come across a thorny bridge. Cross it to find a Fire Shield. Roll into the wall to break it and jump across some crumbling platforms. Slow down after the loop-de-loop for a Water Shield and Super Ring Item Boxes, then jump up to the bridge. If you're playing Tails (or Tails is accompanying Sonic), it is at this point that you should fly up to a platform a little off to the right. Take a break here before flying up to a platform past another platform, which is as high as you should be able to go.
Roll into two Super Ring Item Boxes and take the spring to a new area. After passing two loop-de-loops, you should spot a bridge above you. You can fly up to it or bounce up to it if you have a Water Shield. Ignore the spring and jump over the spikes to the right. Hop over the gap toward a spring that will land you in a pool of water. Walk into the wall to the right to find another spring that will launch you to the second giant ring of Act 2. After the Special Stage, you can exit through the right to meet the stage's final boss.
The Death Egg Robot will target you before it even makes an appearance onscreen. Use a Spin Dash to get out of its sights and the fight will begin. Start by using a Spin Attack to hit its head; if you can't reach above its spiked arms, wait until you reach a hill for some elevation. Dodge the targets whenever you see them as well as its extending arms. The spikes on its fists must be avoided, but its arms can be jumped on to reach its head and get a few more hits in. After six hits, the robot will speed up. Get two more hits in to destroy it. After the fight, a capsule containing some animals will float down from the top of the screen. Hit the switch to free them and clear Green Hill and move on to the next zone.