Sonic the Hedgehog 2/Sonic

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Current Fastest Time

Unless otherwise stated, you should start each stage with a 6 tap spindash.

Emerald Hill 1

Pretty simple stage, just follow the run above.

After collecting the speed shoes, you want to start your roll just as you go through the third ring on the ramp. Ideally you want to land on the left hand side of the invincibility box up ahead, which means you can just hold right for the remainder of the stage. If you hit the right hand side of the invincibility, you're too high and will miss the 10 ring box up ahead unless you hold back a little to adjust.
If you land on the loop with the up-right facing spring, tap left just after hitting it, then switch back to right, which will ensure you don't get stopped by the corner up ahead.

This method almost always gets 0:20, but if all your spindashes are good and you get this jump over the first yellow spring then 0:19 is very possible.

Emerald Hill 2

Again, relatively straightforward, make sure to hold down as you cross the bridge at the start.

Instead of slowing down before the gap, it's possible to jump off the ramp into the monkey and land in the gap at full speed, this can save a second at the end of the stage if it goes very well, but sometimes you'll also stop dead upon landing.
After the checkpoint, jump off the quarter-pipe, letting go of the jump slightly above the top of the ramp, then holding it again before landing on the invincibility box. If done correctly, you should be able to hold right and bounce on the buzzbomber up ahead, land on the spikes and hold right to the boss.

Typical run here is 0:38, but 0:37 is possible with very clean execution.

Chemical Plant 1

Start with a 3 tap spindash and jump.
Make sure you jump at some point so you're running through the first loop, as you want to activate the speed cap when jumping over the spring.
After the yellow blocks, you go through two loops that exit downwards, and a third regular loop - behind the right pillar of this loop is a steep ramp, as you pass behind it, jump, hold right to activate the speed cap and hit the gap in the wall.

This typically gets 0:23, but by rolling and jumping in the sinewaves after the yellow block cycle it's possible to get 0:22. It's also possible to beat the block cycle with very aggressive play at the start of the stage and get 0:20, but it's very difficult and not considered worth attempting at this time.

Chemical Plant 2

Refer to this video for this stage.

Start with a 3 tap spindash and just hold right. You should bounce off the enemy, hit a wall and take off down the slope.
You should see three cross-ramps as you go down this slope - jump anywhere between the second and third ramps you see, then jump off as you approach the top of the vertical slope such that you land in the gap where the door is. If done correctly, the door should open. Make sure to stand on the ramp on the left of the door to activate the path switcher that lets you go to the bottom path ahead.
After a loop comes the big jump up to the top of the stage, which can be made significantly easier by jumping with no direction pressed, and then holding right to activate the speed cap. If you hold right as you jump, your jump will be significantly smaller.
For the last jump in the stage, just mash the buttons after you go off the platform before it.

This strategy typically yields 0:40, but with flawless execution 0:39 is possible as demonstrated in the video above.

Aquatic Ruin 1

This stage has uneven ground throughout, so it's very important to make the jumps in this stage very accurately. The first one should be made just after the ground level dips slightly, which should clear the pillar.
After the loop, jump from behind the right pillar (similar to Chemical Plant 1) and you should land on the log up ahead.
It's worth taking a little extra time to make sure the next spindash is good, as if it's not strong you can get flipped out of it by the spring up ahead, wasting time. Learn when to start holding right again after going off this edge, too.
The next jump is the most difficult in the stage, since both Sonic and the slopes are obscured by leaves in the foreground. The ideal case is a large jump that clears the entire pool of water and lands on the speed shoes from the top, but if you miss that you can save it by landing on the second shark, or just behind the speed shoes. IMPORTANT: no matter what happens, make sure you always hit the speed shoes from the top, since if you hit them from the side, a very unhelpful glitch will come into play: if speed shoes take effect underwater, as soon as you breach the water level they will stop working.
After this there's one final jump through the loop to end the stage, you need to hit the steepest part of the ramp (which is partially obscured again), and pull back slightly before hitting the side of the loop. If you touch it you get kind of "stuck" in the side of the loop and have to make another jump to get over the top of it.

This is the first stage where the times can be quite variable, anything from 0:21 to 0:24 is in acceptable range here.

Aquatic Ruin 2

Refer to this video for this stage.

The key jump in this stage is the underwater one that hits the underside of the pillar and keeps speed throughout the entire underwater section. There appear to be two frames this jump works on, but they're very difficult to see at the speed you travel. A handy visual cue is to watch the bubbles you go past just before the jump: as they hit the very left edge of the screen, hold jump.
On the spindash to the spring to get out of the water, this should be a 1-tap and you should also tap left just before going up. This should regulate your speed well enough that you can hold right and sneak underneath the bugs here.
Not shown in the video above is a glitch that causes the boss to skip its blowing up animation: if you land the last hit on the exact frame the boss starts swinging its hammer it will exit the arena straight away and allow you to get to the capsule about 3 seconds quicker. It costs about half a second over an optimal boss fight to attempt, though
Speaking of which, make sure to jump on an incline when hitting the capsule. Nothing worse than losing a second due to a bad capsule jump.

If everything goes well, this strat generally yields 0:42 or 0:43. Missing the underwater jump is the biggest single mistake you can make, and costs around 4 seconds. Getting the boss glitch saves 3 seconds, but shouldn't be relied upon.

Casino Night 1

A tap jump just as the ground becomes flat again after the first slope should put you behind the speed shoes. If it looks like you're going to hit them, you can save it by holding jump to bounce over the bumpers up ahead.
The blue block up ahead is on the camera timer, so you want to get to it as quickly as possible to make it start its cycle. As it moves upwards, time the jump when the top of the block lines up with this part of the background.
The flipper is where this stage gets tricky. The objective is to launch the flipper slightly after landing on it, such that you land on the platform on the other side of the pit of bumpers. From here, you want to do a two-thirds height jump (the really tricky part) to pass through all of the bumpers up ahead, then another jump to pass underneath the blue block ahead. Sometimes the launch off the flipper goes too high and bounces off the shield box: if this happens, you can still save it by being stopped by the top corner of the ramp in the ceiling, and moving right into the gap as you fall. You need to do this in two bounces or the blue block will stop your next jump, however.
In total you have about one second worth of error between picking up the speed shoes and the jump from the two boxes across the top of the stage. This jump has to reach the top path: missing it costs at least 3 seconds, probably more considering the unreliability of the bumpers below.

If this route is executed correctly, it finishes in 0:28 or 0:29.

Casino Night 2

When jumping to the second speed shoe, pull back a little bit on the jump, otherwise it's possible to clear the box.
After the checkpoint, it's possible to bounce up to the high path or fall through to the middle path. Both are roughly equally fast. If you take the middle path, when holding the second spring down, release just as the top of the spring passes into line with the blue section of wall to the left, and be sure not to hold right to exit until Sonic is entirely over the bumper to the right.
For the last spring in the stage, you want to release jump when the bottom side of the spring is roughly halfway between the second and third last coils of the spring, and then hold nothing. If it works, you should fall straight between the two flippers facing opposite directions at the bottom and be able to spindash to the boss. You'll see two columns of lights near the edge of the platform, jump from between these and you'll make it into the right hand corner of the boss arena.
For the boss, 1-tap spindash, tap left a couple of times and run up the left hand side. Do a full size jump once you hit the vertical part of the slope on the left - if done correctly you should land on the boss and be able to bounce on it for the remaining hits. When doing this, try to make Sonic bounce back towards the middle, so you can keep bouncing on him wherever he moves.
If your bounce is too low and you think you're going to get hit by the boss's claws before you get hit 3, you can use the blue bumper in the centre of the arena to save yourself. This bounce is always sufficient height to get the remaining hits.

A good time on this stage is between 0:59 and 1:01. A solid boss fight is key to this time, as the stage is fairly straightforward.

Hill Top 1

Start with a very fast 1-tap spindash and jump to clear the ramp. Land on the cable platform and spindash - if you spindash from the platform above a spike enemy will spawn right where you land, and you have no rings...
After spindashing into the S-tube, start holding left as you approach the ramp and hit the gap. If you get it just perfect you can land on the right hand side of the ball in the seesaw, but more often than not you should fall to the left hand side and jump over it.
As shown in this video, it's possible to get a super high bounce off the first seesaw here, such that you skip the second one and go to the platform above. This actually has to do with your actions at the start: if you can get Tails to jump straight up like this, he'll fall in the pit trying to follow you and not have enough time to respawn. The game still stores his speed in memory, however, until he drops out of his flying state when returning. When Sonic hits the seesaw, the game actually checks both characters' speeds, and uses the higher one to determine how far to throw the ball up. This saves two seconds if you can pull it off.
Land on the next cable platform, and start running off it as you go through the third ring, facing left to ensure you get knocked back to the right. As the platform falls it takes you with it in your invincibility time. As these three blocks (1) appear in the bottom centre of the screen, hold left to zip out:

(1): Look for the three blocks at the bottom centre to reach this height.

Wait for the platforms underneath you to move upwards a little bit. If you stand still in the same position as the video, as the "earthquake platform" comes up underneath you Sonic will run on the spot, once this happens you can jump into the gap onto the rock and be safe. If you have no rings at this point, there are three at the end of this hallway, but they're in the air so you have to jump for them.

Ideal time here is 0:42 to 0:43, but you can save two seconds over that with the super seesaw bounce described earlier.

Hill Top 2

Mystic Cave 1

Mystic Cave 2

Oil Ocean 1

Oil Ocean 2

Metropolis 1

Metropolis 2

Metropolis 3

Sky Chase

Don't die.

Wing Fortress

Death Egg