To get Knuckles Air Necklace, you must go down the tunnel with a ghost warning sign and a spring at the bottom. You have to be fast underwater or you'll die. Once you have this it makes it possible to find the Lost Chao.
Big the Cat Appearances
There are several places in SA2 that you can see Big the Cat from Sonic Adventure. Here are a few of them:
1. City Escape: About 3/4 of the way down when you're running away from the truck look on the right sidewalk to see him running away.
2. Radical Highway: After going in one of the rockets look at the blimp to the left and he will be sitting on it.
3. Pumpkin Hill: Go to the area where the train is stuck (it's going back and forth) and he is behind one of the gates waving to you.
4. Cannon's Core: With Rouge, go to the top of the highest pillar in the main room and look up. He's jumping up and down.
5. When you're battling against Shadow with Sonic in the Green Forest area there is a grate. Look down in the grate and you can see Big fishing.
Boss Attack Mode
To unlock Boss Attack mode, complete either Hero or Dark side story modes. You'll be able to fight each boss from either Hero or Dark side.
Chao pillow:
Go to a Chao Garden and get a coconut. Then, with a sleeping Chao, pick up the coconut and put it by the its head. The coconut will act as a pillow.
Clone a Chao
You will need 2 memory cards with at least 128 blocks on each. First take the chao you want to clone out on one of the VMUs. The either e-mail yourself a copy (or to a friend) or just copy in the file manager of the dreamcast. The File is Sonic2____VM. Now you have two of the same chao.
Dark Garden for Chao
Take a Chao and raise it with a Dark character. Feed and train it until it cocoons. After it evolves, stairs will appear at the Chao Lobby. Follow them to reach the Dark Garden.
Dupe Chao Warning
For extra Chao, you can put a Chao Egg from SA1 on a memory card and take it out in SA2, but if use use any type of egg besides regular, it might screw up (my Chao became all distorted). Also, it will be a regular caho, not silver, gold, or whatever type of egg you used.
E102 appearance
In Rouge's Inside the Pyramid stage, one of the robots you blow up is E-102.
Egghead Chao !
Just like the pumpkinhead chao, you can also give a chao an egg shell, and he will put it on his head all you have to do is hacth a new unborn chao, then pick up the top part of the shell and give it to a chao that you want to have it, then he will look at it for a few seconds, and then he will put it in his head. Some chao won't even care about them, they will just through it away. If you don't want the eggshell, you have to get it off the same way you do with the pumpkin !
Eggman's mysteroious melody
To get eggman's mysteroios melody.Go to the sand ocean level then on the first moveing platform. Wait until the platform moves to the lefthand side then(with the jet booster)jou fly until you see a platform and fly over to to it and eggman's mysteroios melody will be there. Now you have something to do with those ruions!
Full pause screen
Pause game play then press X + Y.
Hero Garden for Chao
Take a Chao and raise it with a Hero so that it will resemble a Hero. Win a Hero Fruit in the VMU game, then feed it to the Chao. Wait until it cocoons into an angel-like Chao (it will have a halo). Then, take the stairs going up at the Chao Lobby to reach the Hero Garden.
Hero or Dark Chao
To make a Chao a Hero, simply use a Hero character and keep pressing B or X to pet them. If done long enough, it will go white and be a Hero. To make it Dark, just use a Dark character and do the same thing.
Hidden artwork
Put the game disc in a PC compatible CD-ROM drive to find additional images from the game.
Kart racing mini-game
Complete Tails' driving quest in the Hero side story to receivethe kart racing mini-game in the Hero side story. Complete Rouge's chase mission in the Dark side story to unlock the kart racing mini-game in the Dark side story.
Knuckles Lost Chao
Pumpkin Hill: Use the mystice melody, follow the path.
Knuckles' Mysterious Melody
After you have Knuckles' Shovel claws go to the Wind Canyon level and after you ride the wind to the surface, fly to the lonely Mummy's corner. There you will see an egyptian picture with the diggable surface in the border. Go and dig in that border and the mysterious melody will be there. Now you can do something with those blue ruins!
Play Catch with S.W.A.T. BOTs
First, you must have the Magic Hands for Sonic. You find them in the "City Escape" level by using the Fire Ring and Bounce attack on four metal boxes.If or when you do, go to the level, "City Escape," then find a S.W.A.T. BOT. Press the Y button until it says "Magic Hands" in the top-right corner, then press B. When you do, the S.W.A.T. BOT will explode and then appear inside of a little clear ball. Pick the ball up and find another S.W.A.T. BOT. Once you do, throw the balled up S.W.A.T. BOT at it. The S.W.A.T. BOT should shoot the ball and the ball will be sent back to you. After 6 or 7 throws, the balled up S.W.A.T. BOT should blow up and die.
Pumpkin head for Chao
Find one of the Skeleton Dogs; the easiest place to do so is Pumpkin Hill as Knuckles, and combine it with your Chao. As either Knuckles or Rouge, start digging around in the Chao Garden. Eventually a pumpkin will appear. If you give it to the Chao mixed with the Skeleton Dog it will put it on its head. If you want to take it off, either throw or hit your Chao.
You can find pumpkins in the regular and Hero Gardens, and skulls in the dark Garden. Get them by digging as Knuckles or Rouge.
Run on foot
At the start of the City Escape level, instead of landing on the ground with the board, scrape the roads on the board. When on foot run full speed at a wall and get knocked down. Pause game play if you fall after hitting the wall. Choose to restart the level to run on foot and not on the board.
Secret Area
On the green forest level (Sonic), near the end there are three wooden crates (the ones near the green-swamp-creature for your chao). Break them and one is on top of another box. But bounce the one in the ground and you will go to a shortcut. It's easier than the regular path.
Secret level and characters
Collect A ranks for all missions for the following characters and earn the special characters in 2P mode.
Sonic - Amy Rose
Shadow - Metallix (from Sonic CD)
Knuckles - Tikal (from SA1)
Rougue - Chaos 0 (from SA1)
Tails - Chao Walker
Robotnik - Big the Cat (from SA1)
Earn 180 emblems to unlock a new stage - The classic Green Hill Zone from Sonic's Mega Drive debut.
Shadow's Fire Bracelet
In Shadow's Radical Highway level go through the level until you are bombarded by airplanes for the SECOND time. You might see a sign with arrows pointing backwards. There, you sommersault through the cylinder and find the fire bracelet. Now you have sonic's power of the fire sommersault!
Sonic's Magic Gloves
Make sure you have the bounce attack&Fire sommersault before you pull this off. Go to Sonic's first level and go through until after the huge skyscraper fall. There, you may see a floor made of 4 metal boxes. Bounce on the boxes until you fall through. There, you can have the magic gloves. They don't really come to any good use because there is a risk involved changing your Icon to magic gloves being at a certain distance from the enemy--but it sure is fun!
Tip: Planting Seeds in the Chao Garden
If you play through the Chao Adventure 2, the VMU game, you will find seeds at the end of some of the quests. These seeds can be taken to the Chao garden and produce rare fruits. In order to plant these seeds, you need to first win the shovel and watering can in the beginner Chao races. As soon as you have won these, take the seed out of the VMU and give it to one of your Chao. The Chao will take it, plant it, do a little dance and a little weed you appear. Eventually, it will grow into a tree that you can use to help improve your Chao stats.
Unlock Last Stage
In order to play the actual last stage of Sonic Adventure 2, finish both Hero and Dark side story games. Once done, go into story mode and a "Last Stage?" menu selection should appear between Hero and Dark selections.
Unlock Super Sonic and Hyper Shadow
Everybody wants to play as Super Sonic, and now you can. All you need to do is complete "Last Stage?" in story mode, and you'll unlock both Super Sonic and Hyper Shadow.
Wake a sleeping Chao
Sleeping Chao are annoying because you cannot feed them. To wake them up, stand next to it and whistle. You do not have to anger them by picking them up during a little nap.