When you finish Splash Hill Zone, Act 1 you’re given access to the Stage Selection Screen. Finish the three Acts of any of the four Stages to reach the Boss level. Then just beat the boss and you'll unlock this. Refer to the videos below if you're struggling.
You should get this by the time you get all of the other achievements since you will need to beat the game twice to get everything else. If this is the only achievement you haven't unlocked, just replay the Splash Hill Zone until it unlocks.
After you have collected all seven Chaos Emeralds Sonic can turn into Super Sonic by pressing after getting 50 or more rings in any level. While he’s powered up, Sonic is invincible, faster, can jump higher, and can breathe underwater.
For this achievement you must reach the end of Act sign while in Super form in all 3 Acts of the 4 Stages. I recommend doing this while playing each level again on Time Attack Mode to lessen the amount of time to 200, as you'll need to do that anyway for Contender and both this achievement and Contender can only be done after beating the game.
After completing all three Acts and the Boss fight of all four Stages, the final level will unlock. Complete the level, wait for the ending to play and the achievement will unlock. Refer to the video below for the boss if you're having problems.
For this achievement you will need to complete all Acts, Boss Levels, and Special Stages on both Score Attack and Time Attack Mode. Time Attack Mode is unlocked after completing a Stage on Score Attack Mode (the default mode) and can be accessed by pressing on the Stage Select Screen.
After doing all the Stages on both modes, log into Xbox Live and press from the Stage Select Screen. Your results for both Score Attack and Time Attack Mode will be uploaded for that particular level. Then press for the next level and through every level to get the achievement.
Also, note that if you couple this achievement with Golden Flash, it will significantly reduce the amount of time to 200.
Once you have completed the Special Stage it can be accessed from the Map screen like any other level. That said, this is nevertheless a deceptively simple achievement. It may seem like you have plenty of time to collect all the rings but you’ll have to be both quick and accurate in order to get them all in time. This is really just a situation of studying the level and practicing the level. Don‘t forget you can restart the level from the pause menu if you get a bad start or something.
This sounds like a lot at first, but after playing all acts twice and clearing all the special stages you should be close to earning it. Doing Special Stage 1 over and over will net you 3 lives each time.
Here is an easy way to boost it if you need to. This is on Casino Street: Act 2.
Ways to obtain a life
-Collect 100 rings
-Collect 3 sonic cards
-Find an item box containing an extra life.
What you should do is start the level and just run through and collect as many cards as quick as possible. You only have a couple of seconds to collect 3 or more cards of the same item or it will vanish. I wouldn't recommend playing through the whole level. Just play about 2 and a half minutes of the level and then restart the level. Your lives will be saved from the previous run, so don't worry about that. If you think you are about to die, then quickly pause the game and click restart. It may just help you reach 99 live a bit sooner. You also don't lose any lives when you restart a level, unlike previous sonic games.
I only played the Casino level for only 30 minutes, and I managed to gain over 75 lives. So that is an estimate of about 2.5 lives per minute. Each run through would normally net me 3 lives from collecting rings, 3 lives from collecting sonic cards, and 1 life from an Item box. The item box is located near the middle of the level.
To acquire a Chaos Emerald you must get to the end of a Special Stage and touch it. To reach a Special Stage you need finish any Act with 50 or more rings and jump into the giant ring that appears, hovering to the right of the end of Act sign.
While any Special Stage can be reached from any Act you can only reach one Special Stage per Act. I mention this because if you intend to collect all the Chaos Emeralds after finishing the game (which I recommend) you should do it in a backwards fashion, for example:
Mad Gear Zone, Act 1 - Special Stage 1
Casino Street Zone, Act 3 - Special Stage 2
Casino Street Zone, Act 2 - Special Stage 3
And so on.
While in the Special Stage you can restart the level from the pause menu but if your time runs out or you collide with a red exclamation mark circle you’ll have to play the Act again to reach the stage. This is why I suggest using the above method as its easier to mess up on the harder special stages which you will need to replay the levels to reach them again, meaning it would be preferable to replay the quicker, easier levels.
This one is all about practice, take your time and learn the routes. Remember high ground is always the fastest way through a sonic level. If you have already earned Super Sonic you can collect 50 rings on your speed run and change real quick for the extra speed. Here is a video of someone's speed run so you can get a general idea.
This is the hardest achievement of the game. Check the video below if you do not feel like reading.
Run in and jump on the left platform, as soon as Robotnik drops his ball and starts heading towards you jump at him, then do the same again and again. He will then drop his ball to go and do a smash move but if you do another homing attack you will hit him before he can start this move. The important thing is to make sure he is not still flashing white from your first attack so that your hits all count.
This is the method I use everytime and is flawless. Head in and stand a little to the right of the flippers at the bottom (if you stand directly under Robotnik he will pick you up and drop you on spikes). When he heads off to the left jump up and hit him, then as soon as he stops flashing do it again. He will then fly up above where he was before. As he is doing this, spin dash (hold down and press ) up the right wall then jump off (press or ) before you reach the bumper and use your homing move ( when in midair) to hit him and the rebound will send you into a bumper which will send you down to the right flipper which you then flip yourself up on (Press or again) and land on top of Robotnik (going underneath would make you hit his electric attack) and that should be the fourth and final hit.
For an easy first hit run all the way to the right then when the pillars for the area go up jump off around halfway up and do a homing attack. This boss is fairly easy, because the spaces are always near him and there are only four or so easily-visible patterns which you will quickly learn. The only one I always avoid is when he is above you in the middle and pillars all rise straight up. At that point, just stay under him as the attack is hard to pull off and get back into a safe position from. Your final fourth hit will withdraw the pillars straight away so you can go for a riskier move than usual if you like.
Keep holding right and double jumping to get speed as soon as you can. You have two safe positions, very close or far back. Just trust your instincts and you will get through this one with no problem.
Final Form (Round 1):
This guy is a copy of the boss from the end of Sonic 2 but much easier (for now at least) when he is walking towards you jump up and hit him twice (you can hit him more if you want but I'd suggest playing it safe for the achievement).Do regular hits not homing attacks, because after two hits he sometimes puts his hands up and you don't want to be hitting him when he does this because it will damage you and ruin your run. After a few hits he will zoom up into the sky. Stay at the right side of the screen, then move a little to the left just before the countdown finishes. Make sure you give him space when he lands - his landing shockwave can hurt you and make you start over for the achievement. He has one other attack in this form where when he lands he will raise his hands into a straight position (like he's about to go boxing). If he does this just zoom right over into the left corner then go back. After 12 or so hits he will start to frazzle and your hits will not make him flash white.
Final Form (Round 2):
When he starts to go electric and the alarms sound shoot over to the left of the arena. He will always start this round by bounding over, he takes two steps then does giant moon leaps which you can spin dash under,. He usually does three of these before he gets to you so choose your moment well, use your spin dash, and run to the right corner (he will bound back that way, but never reach that corner). He will take off like before and this time stay in the right corner doing a spindash until just before he lands then shoot over to the left corner. He has two attacks from here, the steps we mentioned before or he will shoot his hand up from the far left corner. You can see it going up but it wont hit you, so don't worry. It will come down above wherever you are so I tend to walk slowly towards him then when it comes down hit it from the left side with a homing attack in the air which will propel you towards Robotnik. The reasons for this are that if it lands in the floor it takes three hits which is more chances to accidentally get hit and you have a timer before it returns. Once you hit it, it will fly back and hit Robotnik, knocking him down. Run over and do two normal jump attacks on him (three if you want to be risky) then repeat. After 9-10 attacks he will shoot pink shots at you but these are small and easy to dodge. Occasionally, he will also shoot a laser beam along the floor when his arm is coming down but as long as you avoid the front of it you'll be OK. Twelve hits later he'll fly up and his scanning target will zoom across the screen.
Final Form (Round 3):
Stand in the middle of the zipping target zone and wait to see where it ends up. Stand roughly five Sonics or so from either side of that area then get ready to jump when Robotnik hits the floor and use a homing attack on his head and bam. Once you do that, you're done. If his floor hit hits you you have a chance to recover just jump and hit him as soon as possible, but be quick (this is why we want to be close to him).