*There are 16 Hero stages, 14 Dark stages, and 1 Last stage, with 5 missions per stage.
Welcome to Sonic Adventure 2. This is the second re-release of a game that originally came out on the Dreamcast over a decade ago, and like with the first re-release there have been a few changes. The visuals have received a bit of an upgrade and a few of the A-Rank requirements have changed slightly, but mostly it's the exact same game.
Step 1: Complete Story Mode
In this game the story is split up into three parts: the Hero side which tells the story from Sonic's, Tails', and Knuckles' point of view, the Dark side which tells the story from Shadow's, Eggman's, and Rouge's point of view, and the Last story which picks up after the Hero and Dark stories to wrap everything up. You can play either the Hero or the Dark story first or you can go back and forth between them to play the game chronologically, your choice, but you must complete them both to unlock the Last story.
When you're done this step you will have unlocked Hello World, HERO!, DARK!, and Beyond Good And Evil, and you will be at 34/180 emblems.
Step 2: Kart Race and Boss mode
You might as well get these out of the way next. You unlock Kart Race upon completion of Tails' Route 101 stage or Rouge's Route 280, and it becomes available to you in multiplayer after completing both. You unlock Boss mode after beating either the Hero or the Dark story, though you must complete all three stories to have all three boss modes available to you.
When you're done this step you will have unlocked Boss Attack and Speedy Racer, and you will be at 40/180 emblems.
Step 3: Stage Select
This is the majority of the game. After completing Step 1 you will be done 31 missions, meaning there are 124 left to go. Refer to Emblem Mania for a guide on completing and A-Ranking every mission.
When you're done this step you will have unlocked Mission Complete, Emblem Collector, and You Are The Legend, and you will be at 171/180 emblems.
Step 4: Chao World
Though I've left this step for last, you'll want to start raising your Chaos pretty much immediately. You don't want all the chaos drives and animals you pick up during the stages to go to waste, plus sometimes you just need a break from the missions. For all necessary Chao-related information, refer to Karate Master.
When you're done this step you will have unlocked Chao!, Chao Raiser, Heaven or Hell, Karate Master, and Emblem Mania.
All that is left for you now is the random multiplayer achievement that they threw in, Level 4!, and you're done. The game has aged surprisingly well and is still a lot of fun to play once you get back into the groove of things, and hopefully the achievements will be enough convincing for some of you to go all the way this time around.
[x360a would like to thank dakisbac for this roadmap]
Boss mode will appear in the single player menu after completing either the Hero or Dark story, but you won't have access to all three boss attacks until you have completed all three stories.
Hero Side pits you against all the Hero story bosses, Dark Side against the Dark story bosses, and All, as you might expect, against every boss in the game, including The Biolizard and The Finalhazard. There are no breaks between these bouts so if you had any difficulty with any of the bosses you should stock up on lives before you start. Additional information regarding the bosses can be found here.
This will unlock after completing all three boss attacks.
For this you must A-Rank all five missions for any one stage. As you only play the first mission in story mode you must do this through Stage Select. Completing one mission unlocks the next.
The easiest stage for this is Tails' Route 101. The requirements for this level are as follows:
Mission 1: Chase the President's limousine!
A-Rank: Finish in under 2:45
Mission 2: Collect 100 rings!
A-Rank: Finish in under 1:30
Mission 3: Don't hit other cars!
A-Rank: Finish in under 3:00
Mission 4: Don't hit the walls!
A-Rank: Finish in under 3:00
Mission 5: Clear Hard Mode
A-Rank: Finish in under 2:50
The key to this stage is to collect as many rings as possible (since you get a boost for every 20 you collect) and to avoid hitting the walls or other vehicles. The only A-Rank that's not really a gimme is surprisingly the first mission; you will undoubtedly A-Rank the other missions just by completing them. If you didn't A-Rank the first mission on your first try then you will definitely be able to go back and do it once you've completed mission four.
You will unlock Hello World after completing either the first Hero stage (City Escape as Sonic) or the first Dark Stage (Iron Gate as Eggman), HERO! after completing the entire Hero story, and DARK! after completing the entire Dark story.
Completing both the Hero and Dark Story unlocks the Last story, and this achievement unlocks on completion of the Last story.
Kart Race will appear in the single player menu once you have completed either Tails' Route 101 or Rouge's Route 280. It will appear in the multiplayer menu once you have completed both.
Unlike the boss attack achievement, this only requires you to beat the Expert track instead of all three, though if you are going for all the emblems you will have to do all three regardless. For this I recommend using Knuckles as he seems to be the best rounded character.
I have all the other Chao-related achievements referring here just so all Chao-related information is in one place.
Step 1: Gain access to Chao World
You will want to gain access to Chao World with at least one character from each side. To gain access to Chao World you need to find a Chao Key with that character in one of their stages. There are three (blue) Chao Boxes per level - you need only smash one of them (not necessarily the first) to grab the key.
Step 2: Raise a Hero and a Dark Chao
Now that you have access to Chao World you want to start raising two Chaos, one which will become a Hero Chao and another that will become a Dark Chao. Go into the garden and hatch your eggs either by smashing them or waiting for them to hatch.
Easy things first, take one of your newborn Chao out of the garden and into Chao Kindergarten. Once there take it to the Fortune-Telling House to give your Chao a name. The game will suggest a name for you which you can accept or reject. If you reject, the game will prompt you for another random name. You can reject again to name the Chao yourself. Either way, once your Chao has a name you will have unlocked Chao!
Now you start the fun (more like monotonous) task of raising Chaos. Pick one to raise only with Hero characters so that when it evolves it becomes a Hero Chao, and raise the other with only Dark characters to get a Dark Chao. You don't actually have to raise their stats at all - they evolve once you've spent three hours in your garden - so all you need to do is shift their alignment before the evolve. You can do this by petting them or feeding them with a character from one faction or by treating them badly (ie, jumping on them) with a character from the opposite faction. You can check their alignment by taking them to the doctor and looking at their medical chart.
Once both of your original Chaos have evolved into a Hero and a Dark Chao you will unlock the Hero and Dark gardens, Hero and Dark races, and Heaven or Hell. Now, unless you feel like doing double work, you have no further use for these Chaos. Go to the Black Market (in Chao Kindergarten) and buy a new egg.
Step 3: Raise a Neutral Chao
You want to raise this new Chao into a Neutral Chao. The reason for this is that Neutral Chaos can participate in both Hero and Dark races. As soon as it's hatched take it to the doctor and look at its medical chart. As you've seen here before, this chart details your Chao's alignment, but more importantly it ranks your Chao's stats (Swimming, Flying, Running, Power, and Stamina) from E to S. Though it is fully possible to beat everything with a Chao that has an E-Rank in Running, if that's what you have then just go buy and hatch a new Chao. Note that every time your Chao evolves the stat you raised the most will go up a grade, but the goal is to have it evolve only once to complete all the races and karate so it's easier to just get a new one.
What do these grades mean? Whenever you give an animal or Chaos drive to your Chao one or more if its stats will raise. Once the all the percentage bars get filled in that stat raises a level, and the amount of points you get added to that stat's point total depends on your grade. For example, if you have an E in running and an S in power, when you level up running you might get 16 or so points but when you level up power you will get 26+ points. It's your points total that determines how well your Chao does in races and karate. The level is basically just a limit to how many times you can level up the stat in that lifetime (level 99 is the max, so 99 times).
Step 4: Levelling up your Chao
As for actually raising your Chao's stats, here's what you'll want to do. First, take your Chao to the Hero garden. In this version of the game, there is a glitch with the fruit in the Hero garden that causes each bite of the fruit to give 20-30% instead of the intended 10%. Use this to raise your Chao's stamina very quickly. For the other stats you will want to rotate between the following three legendary animals:
Swim +20%, Fly +4%, Run +8%, Power +32%
Location: Wild Canyon. Take the wind lift up then fly left to the very end. Climb above the statue then dig into the room where the Mystic Melody upgrade was. Dragon is in the top corner to your left when you enter. Takes about 25 seconds to get.
Swim +12%, Fly +32%, Run +4%, Power +16%
Location: Metal Harbor, in the third Chao box. First box is on a separate platform to your right by the first trail of rings you can light dash. Second is on the hangar in one of the alcoves to your left before the third trail of rings you can light dash. Third box is on the platform where you take the rocket to the missile launch. Takes a little over a minute to get.
Swim +16%, Fly +12%, Run +36%, Power +0%
Location: Dry Lagoon. Take out the two GUN robots hassling the turtle then ride him to the big oasis. Jump onto the island where there is a circle of stakes. Stand in the middle and whistle to get the unicorn to jump out at you. Takes about 20 seconds to get.
These animals (especially the Phoenix) take some time to get, so you don't want to have to go back and forth between Chao World and these levels to get them. Thankfully you don't have to, due to another glitch that allows you to use animals and Chaos drives infinitely many times. Here is a video explaining how to do that:
(you can skip ahead to 2:08 in the video)
The best characters for this glitch with are Tails and Rouge. Eggman is just too big and annoying, Knuckles' hands are too big and annoying, and I found that Sonic and Shadow accidentally somersaulted the Chao too often.
Since you're not bothering to up the grade of your stats, you'll basically need them all maxed out to win all the races and karate. To give you an idea, here were my Chao's stats when I finished:
Swim - B - level 99 - 2189
Fly - C - level 83 - 1593
Run - E - level 99 - 1270
Power - S - level 99 - 2764
Stamina - D - level 99 - 1569
My Chao dominated karate but struggled with the races, the running only-races in particular since it couldn't compensate with its other stats. The Jewel race Peridot level 5, for example, I only won by using all my stamina and only because the one Chao that was winning tripped (I had to retry repeatedly until this happened). So again, if you have an E-Rank runner then start with a new Chao.
If you're going for this achievement you will unlock all the others along the way.
Complete story mode (3)
Complete boss attack (3)
Complete Kart Race (3)
Complete all missions (155)
A-Rank all missions (7)
All Sonic's missions
All Tails' missions
All Knuckles' missions
All Shadow's missions
All Eggman's missions
All Rouge's missions
All Cannon's Core missions
Chao Race (5)
Chao Karate (4)
After completing the three story modes you will have only unlocked 34/180 emblems so decide early on if you want to go for this achievement or not.
The two big time commitments here are A-Ranking every mission and raising a Chao to a point that it can win every race/karate tournament. Completing all five missions for each stage doesn't take long, but you do not want to complete them all and then go for the A-Rank separately - that would be doubling the amount of work you need to do.
There is an excellent video guide for A-Ranks with commentary here:
You can pretty much follow what he does for your A-Ranks, though many times you can (and sometimes should) opt for alternative paths as he cuts some of them pretty close.
I have posted some additional tips regarding the hunting missions here.
It's also worth noting that there is an extremely easy way to A-Rank the Cannon's Core missions if you're not above using glitches, which is detailed here.
For details regarding the Chao-related emblems refer to Karate Master.