You may have first noticed some Red Star Rings in some levels of the game as you played through each Act for your first time. There are 90 of them in total, 45 for each Sonic, of course, and all of them are required to unlock an achievement. For Classic Sonic, you might want to play the specific Challenge Act from City Escape Zone to get the Thunder Shield Skill, which will grant you a double jump; this will make getting some of the Red Star Rings a bit easier to obtain. Although a text guide can be more useful for some, it should be easier for you to just watch a video on where these special rings are.
Sonic Generations | Red Star Rings
Green Hill Zone
These rings will not appear until you beat Green Hill Zone (Act 2) for the first time.
Right at the start of the level, you should come across a bridge with three fish jumping over both sides. In the middle of these two sets of fish is the first (1/5) Red Star Ring, sitting in plain sight.
Shortly after this, you'll reach a point where you have to hit two crab enemies to encounter a flying purple bug. Wait until it's close to the high ledge to the right of it and jump onto the bug to gain enough height to reach the ledge. Simply continuing on this path will give you the next (2/5) Red Star Ring, just sitting inside a corkscrew.
Continue across the large jump (which you get across by use of a spring), and drop down below after hitting a checkpoint. If you're going the right way, you should be underground, and will have to use a moving wooden platform to get across a few sets of spikes. Jump on the springs on the other side of these spikes, which will place you just before a breakable rock and a curving tunnel. The ground just outside of this tunnel collapses shortly after touching it, so you'll want to jump as soon as you're in the middle of it to get over a spring that'd otherwise send you backwards into the hole below. If you've managed to do that right, you'll be very close to the third (3/5) Red Star Ring.
Continue forwards and jump onto another wooden platform that swings to the right. Yet another platform is at the end of its swing, but the (4/5) Red Star Ring above them is a higher priority than successfully jumping to it.
After traversing this area and running down a curving bridge, some more springs will launch you up in the air towards a yellow bug and a small ledge for you to stand on. Try to land from the spring onto this small ledge; you can return to the spring if you miss. From here, use the bug to gain some height and get to the higher ledge to the right of it, just like with the second Red Star Ring. Just ahead of here is another bug and a yellow spring hidden in a tree. Defeat the enemy if you wish, but you can just ignore it and jump into the spring from a higher position to the left. The final (5/5) Red Star Ring will be waiting for you up there, and with it, you'll get an achievement for finding it.
For collecting all five Red Star Rings, you're awarded with the Treasure Scanner Skill, which will let you see hidden items and springs easier.
Chemical Plant Zone
To get all five rings on this level, you'll have to go through both the higher and lower paths. This shouldn't be too bad, though, since it's not exactly a long level. The high path has three of the five collectibles, so we'll start there. Once the level begins, use the moving platforms just ahead to get to the higher of the two twisting tubes to ensure that you're on the high path. Very shortly after you take the path up, you should find the first (1/5) Red Star Ring between two sets of pipes carrying blue chemicals.
Continue past a checkpoint gate and stay high; you'll know you're going the right way if you come across two vertically shifting platforms with two ring containers and a speed power-up to the right of them. Use the platforms to reach the path up ahead and jump to the stationary platforms to the left. These ones won't move or collapse or anything, so you don't need to rush any jumps. The second (2/5) Red Star Ring will be up in the air between two sets of platforms.
Keep moving with this high path, and you'll be pushed down a waterfall tube after reaching a checkpoint gate. Jump near the end of the waterfall to avoid a gap at the end of it. This is a continuation of the high path, so messing up the jump would void your chances of getting the third high path RSR. After a long vertical climb using platforms and yellow springs, the last (3/5) Red Star Ring of this run will be in plain sight near the last spring.
Now that those three RSR's are out of the way, it's time to get the other two. Avoid the high path at the start of the level and use the low one, hitting a red spring shortly after using it. This should take you to the left, where you'll find a (4/5) Red Star Ring floating above a pipe.
After a bit more of moving through the level, you should be back at the high path, where the first checkpoint gate was during the previous playthrough. Continue on this path until you get to the area the second RSR was at, but jump into the water this time. This drop should take you to a small pit of water with a yellow spring to the right of it. After climbing a few sets of yellow blocks, use the upcoming red spring to move upwards, and make a small jump up the curved corner ahead to reach another closed-off pipe. Break it open and you'll be taken to a pink-chemical-filled room. Simply continuing to the other side should allow you to see the last (5/5) Red Star Ring at the end of this chamber. Collect it and finish the level to complete your collection.
For collecting all five Red Star Rings, you're awarded with the Breath Holder Skill, which allows you to stay underwater for longer.
Sky Sanctuary Zone
This set of Red Star Rings will require you to beat the Act on all three separate paths, which each have their own RSR at the end. The first two RSR's, however, are obtainable without any hassle. Just at the start of the level, you should come across two partially blue square stone platforms, which are placed a bit to the right after a set of spikes on the ground. Jump from the second one to a cloud, which gives you enough height when bounced on to reach the first (1/5) Red Star Ring.
After using a teleport to reach a higher area, you should eventually find a yellow spring, guarded by a standard Egg-Robo. This spring takes you to another cloud, and the second (2/5) Red Star Ring will be floating in the air up in the chain of clouds ahead.
If you make it to the top of the circular platform just ahead of the checkpoint gate, you may as well try to use the Egg-Robo ahead to reach the next cloud before it disappears. This leads to the high path (remember, you need to play all three paths at least once), but you can always just do that later. For now, we'll follow the lowest path. Continue through the level until you get to this point:
As you can see here, this rotating stone platform has a nicely sized hole in it. Falling through starts the low path, leading to its (3/5) Red Star Ring. Playing through the level the exact same way, except not falling down to the path below, will send you to the middle (4/5) Red Star Ring at the end of the level. For the last one, return to the place below, which will be earlier in the level than the split in the picture above.
If you can make it to the top of the rock platform Sonic is on in this picture, you could try to jump onto the Egg-Robo and use the momentum to reach the cloud ahead, leading to the high path. This cloud in particular disappears quickly, though. If you can't make it, don't worry; there's an easy way around it. Drop down to the little mechanical circular platform on the low/middle route, and use it to rise up and to the left until you reach the high path. It's a pretty sneaky maneuver, and allows you to completely disregard the previously mentioned Egg-Robo and cloud. As long as you don't drop down to the two lower paths, you'll end the level by collecting the fifth and final (5/5) Red Star Ring for this Zone.
For collecting all five Red Star Rings, you're awarded with the Twin Spin Attack Skill, allowing you to attack in mid-jump.
Speed Highway Zone
This set of RSR's will require two runs of the level. Run through Speed Highway until you ride a rocket to another part of the level; none of the Red Star Rings appear before that point, so you can just rush the first third of the Act. Drop down as soon as you can after the checkpoint gate and jump up some vertically moving platforms until you can jump into a hallway on the right. This should take you to a fairly wide drop down, with a single enemy in the air. Try to hit it and stay on the left side of this drop, and use the curved piece of the landscape to jump into a tall column with yellow windows. A (1/5) Red Star Ring will be floating in the air very shortly after you land, and the second (2/5) Red Star Ring will be just up ahead, under a bell. You can't miss these two; they're in plain sight.
After riding the helicopter, take the high path by using a booster, and you'll see another (3/5) Red Star Ringat the end of the jump, to the left of the high path's checkpoint. Both the higher and lower path meet up together immediately after the checkpoint, so if you accidentally take the lower path, you should be able to jump behind the higher checkpoint to get it. The last (4/5) Red Star Ring of this run appears in front of another boost ring at the very end of the level, and it doesn't seem to be missable.
For the last (5/5) Red Star Ring, ride the rocket and get to the area described above, where there's a large gap with an enemy, and yellow windows to the left. This time, stay to the right side and drop down as far as you can; you'll know you're going the right way after you use two yellow construction pieces to fling yourself towards a new checkpoint. After ducking under a low roof, the last RSR will reveal itself to you, and will be floating next to some spike balls.
For collecting all five Red Star Rings, you're awarded with the Power Sneakers Skill, which just makes you run faster. These are pretty useful, so if you don't tend to use Skills, you may as well at least use this one.
City Escape Zone
For the first (1/5) Red Star Ring, you're going to want to take the high path all the way through to the next checkpoint. Find a yellow spring near the start of the level that takes you to a balcony in the backdrop, and continue on that path until you get to a rooftop. You should automatically curl up in a ball and grind down the following rooftops, and get the first RSR by doing so. Once the GUN truck is side-by-side with you, stay ahead of it and try to get to the floating (2/5) Red Star Ring before the truck destroys your chances of getting it. You'll then want to scale the platforms to the right of this area and acquire the skateboard power-up as soon as you can; the truck will come back around to destroy it as well, so you'll have to be quick about it. Try to jump into the boost rings past the next checkpoint, and then jump from the platform they send you to into the next (3/5) Red Star Ring. Stay on the high path here (this is the most frustrating part of the RSR run, if not getting to the high path in the first place) and press when prompted to on the ramps; doing so twice will take you to the fourth (4/5) Red Star Ring. The GUN truck should chase you directly from behind soon; make a mad dash to the right and into the boost ring up a few ledges so you can reach the platforms on the right before they get run over. The last (5/5) Red Star Ring will be fairly close to where you land after you use the boost ring; if you miss the chance to get it, you might still be able to drop down the sides of the ledges of the platforms to reach it. These five Red Star Rings can be quite a pain to get, and Act 2 isn't much of a fun experience, either.
For collecting all five Red Star Rings, you're awarded with the Boardmaster Skill, granting you a skateboard whenever you feel like it.
Seaside Hill Zone
At the start of the level, you'll come across your first enemy. Defeat it and stay on the far left side of the ledge just ahead of where it once was, then charge up a spin dash and jump as far to the right as you can. If done correctly, you'll land next to two ring containers and a speed boost. Continue using the high path to get shot through a cannon, and stay on the high path until you drop down to the right of the first (1/5) Red Star Ring and an extra life.
The platforms you've likely landed on move up and down periodically, and it's a bit of a ways until this water section ends from here, so you should return to the air from where you are after you collect this ring. Very soon after you make it out of the water, a mechanical fish will occasionally jump out and snap its jaw a few times. You're going to have to jump into it when it's at a proper height to use it for momentum to reach the small platform ahead, leading to another cannon. Riding this one will shoot you directly into the second (2/5) Red Star Ring. From there, any path you take should lead to the same checkpoint; the only difference is the amount of time it takes to get there, with the highest path being the shortest.
Past the next checkpoint is a moving orange/white platform. Jump to it when it's at the right side of its horizontal movement cycle so you can get the proper distance require to reach the next two platforms, and use the cannon ahead. All of these three platforms will quickly collapse after being touched, so you'll have to be quick about it. Wait for the enemy past a yellow spring to use its electric attack before using it to continue to the right (don't fall into the cannon below) to use yet another cannon to progress into the level. You'll land in a circular pit, and the next (3/5) Red Star Ring will be sitting high up on the right side. Charge up a spin dash to reach it, and then use the platforms to the right of it to reach the cannon above where the RSR used to be.
Once you land, another collapsing platform will be moving up and down above some water coming out of a tunnel. Either stand on the platform for a little while or just run underneath it so you can use the cannon on this alternate path, taking you into an underwater section after going through a loop. Two flimsy poles will help you break your momentum, and the fourth (4/5) Red Star Ring is going to be hiding in the path of a spike ball; time your release of the pole wisely, so that you pass through the RSR and avoid the spikes.
During the final portion of the level, where several circular boulders will start to chase you towards the goal post, some boost rings will appear after you have to climb a few sets of square blocks. Use these, and the next set of boost rings ahead, so that you land on some more orange collapsible panels. There are two more different sets of boost rings very shortly after this, and you'll need to use the higher ones; these will send you through a corkscrew with the last (5/5) Red Star Ring at the end of it, and the end of the level will follow immediately after you get it.
For collecting all five Red Star Rings, you're awarded with the Invincible Start Skill, which lets you start levels with a bit of temporary invincibility. It doesn't seem all that useful, since the start of any level isn't supposed to be all-too-difficult anyway.
Crisis City Zone
At the start of the level, you'll soon encounter a lone flying enemy. Jump towards it and attack it, and bounce up to the higher path to the right. There's going to be a curve up ahead, and you'll need to dash as fast as you can upwards to reach an even higher path, where the first (1/5) Red Star Ring resides.
Later in the city, after climbing the remains of a circular tower, you'll ride a rail leading down to a downward-sloping building that's been toppled over. At the end of this run, some collapsible platforms will start to shake before falling down; jump on the platform to the far right as soon as you can, and ride this high path all the way until you reach a weird angled piece of concrete with a fire spout at the bottom. Safely drop down once the fire recedes, and jump past the small curved piece past it. At the end of this short piece of land, you should be able to see a very small platform to the right; Make your best attempt to jump to it, and then use the moving platforms to the right of it to reach a red spring, leading to the second (2/5) Red Star Ring. This is an extremely frustrating set of jumps to make, and missing it (or falling at any point before reaching the next RSR) means that you'll have to return to the last checkpoint or restart the level.
After a little while, you'll come across your first set of floating debris. A small chunk of pavement will be continuously rising up and down, just to the right of the second piece of debris and to the left of a flying enemy. Hop on top of it, and you'll be able to jump from there to the third (3/5) Red Star Ring towards the next building.
Within a few seconds of moving through the building (whichever path you take to get inside), Sonic will trigger the power of Iblis (the fiery tornado), who will start causing gusts of wind. Carefully make your way to the lower portion of the building and time your jumps wisely, so that you can collect the next (4/5) Red Star Ring without falling off to the right to your doom.
The final (5/5) Red Star Ring is going to be much more within plain sight than the other four have been. After making your way across more debris, you'll eventually have to use either a yellow spring, or the two bouncy springboards to the right of it. The RSR is going to be directly to the left of the cannon just ahead, and its' not much of a challenge to get to.
For collecting all five Red Star Rings, you're awarded with the Hercules Muscles Skill, letting you push movable objects faster. Too bad this isn't Marble Zone.
Rooftop Run Zone
Start the level as usual and pop the first set of balloons that sends you towards a purple enemy. Just above him is a green platform, with another one that moves to the right of it. Jump from the moving platform to the concrete one to the right, and then use the enemy nearby to bounce into another set of balloons to land on a basket. Jump to the next basket as you approach it, and quickly jump from it towards the first (1/5) Red Star Ring.
After reaching a checkpoint by using three sets of balloons, a purple enemy will be guarding a basket; defeat him and hop on top. To get this next RSR the way you're intended to, you need to jump from this basket to the next, but I have never been able to get the timing right myself. If you mess this up, don't worry about it, because you can just go backwards to get to it. Run over to the other side of the room and get on a green platform to the right of a red one. These will collapse after a while, so you'll want to time your jumps as you stay aware of the giant blades' swings. As long as you get to the second (2/5) Red Star Ring, you won't have to repeat the level for this one section.
When you enter the large barrel warehouse, pass the checkpoint inside and continue to the right until you reach two green platforms moving up and down. Scale these two, and you'll have bypassed the much harder way to get the (3/5) Red Star Ring floating above a button. Pressing it opens up a room with a yellow spring that you can use as a shortcut.
Outside of the building, you'll eventually be shot upwards with a red spring to a green platform that hosts a set of balloons and a giant blade. Use the balloons to get through the opening in the building to the right and drop down immediately. Once you enter the base of the giant clock tower, climb up it and you should find the fourth (4/5) Red Star Ring naturally as you ascend; just make sure you don't use the yellow spring to the right of it until you grab it.
When you finally reach the clock's face, use a spring on the right side to get onto a set of platforms that leads to an enemy. This enemy is the only way you can reach the last (5/5) Red Star Ring, so be careful when you use it to gain the extra height.
For collecting all five Red Star Rings, you're awarded with the Long Spin Dash Skill, which gives your Spin Dash more distance.
Planet Wisp Zone
Time to get the last of Classic Sonic's collectibles. Upon starting the level, do a spin dash to run up to the side of a set of spikes. Jump over them and defeat the enemy, and then defeat the one just up ahead. Stand on the far left side of the platform that the second enemy was on and charge a spin dash to make it as strong as you can, then jump as soon as you release the move. This should cause you to bop another enemy and hit a decoy spring; keep holding right to fall onto a small collapsible platform, and quickly jump up to the small room to the right. Grab the Spikes power-up and use it to safely traverse the gap to the right and grab the first (1/5) Red Star Ring.
Once you use a yellow spring at the top of the next room, use a spin dash and jump as soon as you can, just like before, to use the high path as soon as you enter the building. This should take you to a room with two enemies and another (2/5) Red Star Ring, and getting to it should be pretty self-explanatory.
To the right of this room is a big gap and a collapsible panel just in sight above it; jumping to it is the most difficult part of getting the five RSRs, so you might have trouble with this. When you make it to the other side, quickly stay to the right on stable ground. The panel will return after a few seconds, so you can jump on top of it once more to continue ahead. The third (3/5) Red Star Ring floats above a quarter-circle piece in a corner, and you can only get to it by spin dashing up to it. When you get it, use the high path by jumping across the small set of collapsing panels to the right and bopping an enemy, then use a set of moving green platforms to reach another Spike power-up. With this, you can get to the (4/5) Red Star Ring above you by sticking to the walls.
Later on in the level, you'll have to press a switch to activate three moving platforms in a room where a blade continuously moves back and forth. Past this room, after a long curve upwards, a bridge will seal off the level behind you after you reach the top. Jump to the Spike power-up ahead and use it, hugging the ground as you move to the right. This will set you on course to use the lower path and reach the last (5/5) Red Star Ring. In this path, you'll soon find yourself next to three missile launchers, a Spike power-up, and a pink gear. Use the power-up to activate the gear, and jump from the gear towards the final RSR. With the last of the Red Star Rings in hand, you just have to finish the level to complete this half of the collection.
For collecting all five Red Star Rings, you're awarded with the Homing Attack Skill, which lets you do exactly what you think it'd let you do. This Skill requires 100 Skill Points to use, so you can't combine it with anything else.