Sonic Adventure 2 is the first game appearance of Shadow the Hedgehog and the beginning of the Shadow the Hedgehog series. A sequel was made: Sonic Adventure 2: Battle.
It begins with a Military helicopter (Sigma-Alpha 2) flying over the city. "Hedgehog captured", the pilot said. Suddenly he starts shouting "Hedgehog is escaping! Repeat, hedgehog is escaping!" At that moment, Sonic the Hedgehog jumped out of the helicopter, ripping off a piece of the wing to use as a snowboard, and then jumped off. After he destroys a Military Fighter, he encounters a near look-alike of himself named Shadow the Hedgehog who has stolen a Chaos Emerald from the bank a while earlier. Sonic realizes that the military has mistaken him for Shadow. Shadow proceeds to use the emerald to transport to a different location, and Sonic is arrested.
At the same time, Knuckles the Echidna and a mysterious character named Rouge the Bat are fighting over who owns the Master Emerald. Dr. Eggman tries to steal the Master Emerald, but Knuckles stops him in his path by breaking the Master Emerald into pieces. Knuckles and Rouge have a hunt for the pieces of the Master Emerald. Knuckles finds the first three pieces in Wild Canyon.
The next day Miles "Tails" Prower comes to Prison Island in search of Sonic, rescuing Amy Rose from Dr. Eggman in the process. Then Amy frees Sonic from his Prison Cell, and Sonic escapes on a missile. Knuckles leaves Wild Canyon, and heads for Pumpkin Hill. There he finds three more pieces of the Master Emerald. Knuckles leaves Pumpkin Hill, and heads for the Aquatic Mine. Meanwhile, Sonic gets weary, jumps off the missile, and lands on a small island in a vast jungle. There he confronts Shadow once again.
He soon discovers the jungle is going to explode and leaves just in time. When they get back, Eggman was on T.V. everywhere and it is revealed he was being taped from the old space colony, ARK. Suddenly half of ARK comes off, revealing a long pointer called the Eclipse Cannon which shoots out a powerful beam and destroys half of the moon. A timer on screen appears saying 24 hours till the destruction of Earth. Later, Tails discovers Space Colony ARK and the massive power of the Eclipse Cannon. He has to find Sonic, tell the President, and escape the military all before it was too late. He eventually finds Sonic, and escapes the military.
Meanwhile, Knuckles finds the last three pieces he can find of the Master Emerald in the Aquatic Mine. He later pops out of a manhole beside Tails, who is talking to Sonic and Amy over a phone on loudspeaker. Tails chases down the President, then he and Sonic tell the President about the situation they are in. Sonic, Knuckles, Tails, and Amy then head for Dr. Eggman's "secret" base inside the pyramid. Sonic breaks through the security system. Knuckles then has to find three keys to get into the rocket room. Knuckles defeats King Boom Boo, the king of ghosts. After that, Dr. Eggman appears and summons the Egg Golem, which Sonic has to take care of. As soon as he is defeated, they blast off in the rocket.
In all the excitement of the shace ship, the cargo bay opens releasing the peices of the Master Emerald Knuckles had collected. Sonic remarks that only the Master Emerald peices were inside there, Knuckles thinking quickly takes control of the ship causing it to spin out of control. Knuckles jumps ship and lands on a small planet and finds the pieces he lost, leaving Sonic, Tails, and Amy screaming on the ship which then crash lands into the ARK. He defeats Rouge and gets the rest of the Emerald. Meanwhile, in Space Colony ARK, Tails is heading for the engine of the Eclipse Cannon. He destroys the engine, so it's up to Sonic now. Amy gets kidnapped by Eggman and demands the last emerald in exchange. Sonic, who has a fake chaos emerald, makes it to the central control room. Sonic is shot out of an escape capsule that was going to explode in the middle of space.
All Tails, Amy and Eggman can see is a capsule blowing up, so they thought Sonic was killed. Tails is so riled up that, in a burst of anger, he defeats the Doctor. Meanwhile, Knuckles (with the full master emerald) spots Sonic coming out of a portal. Sonic tells Knuckles how he used Chaos Control to save himself, and speeds to the Eclipse Cannon. Sonic confronts Shadow one last time, and destroys the Eclipse Cannon. Tails, grieving over Sonic's "death", looks out the window and sees Sonic at the tip of the cannon smiling.
It begins with Dr. Eggman infiltrating Prison Island in search of the Ultimate Life Form A.K.A. Project: Shadow, a weapon created by his grandfather, Gerald Robotnik. He finds Shadow and using a Chaos Emerald, and the password M.A.R.I.A., he soon discovers that he is a hedgehog. So, he mistakes Shadow the Hedgehog for his enemy Sonic the Hedgehog, and nearly fights him. Then Shadow proves himself by defeating the military guard fighter. After Shadow defeats him, he leaves, heading for Space Colony ARK and tells Eggman to bring more Chaos Emeralds and meet him on the ARK.
Meanwhile, Rouge the Bat is fighting with Knuckles over who truly owns the Master Emerald. Dr. Eggman uses this to his advantage, and take the Master Emerald. Knuckles stops him by breaking the Master Emerald into pieces. Rouge and Knuckles have to hunt for the pieces of the Master Emerald. Rouge finds three pieces in the Dry Lagoon.
Later, Dr. Eggman goes to his base to check up on things, and watch the replay of the news. He finds out that the G.U.N. robots are guarding his pyramid base. He destroyed them and went on inside. While he is watching the replay of the news, he discovers that Shadow had stolen a Chaos Emerald from the Federal Reserve Bank yesterday with everyone mistaking him for Sonic. The scene changes to where Shadow is leaving the bank when he has a flashback of what happened on Space Colony ARK with him and his friend Maria Robotnik. He proceeds to speed down the highway, destroying any robot that gets in his way.
He later sees Sonic, explains to Sonic who he is, and leaves. The next day, Rouge decides to infiltrate Dr. Eggman's base. To do so, she has to find three keys. Meanwhile, Dr. Eggman and Shadow are on board the ARK. Shadow tells Eggman about Space Colony ARK and the power of the Eclipse Cannon. He then puts in the two Chaos Emeralds. They returns to the base at the time Rouge finds the last key. Rouge persuades her conditions to Eggman into helping her by giving him a Chaos Emerald, and telling him where three other emeralds were. Before the deal is closed, she introduces herself to Shadow.
Shadow, Dr. Eggman, and Rouge headed for Prison Island where the three Chaos emeralds are. Dr. Eggman breaks through the security system, and defeats Tails, who happens to be there. Rouge finds the three Chaos emeralds and defeats another Military Fighter. Shadow rushes through the jungle, plants the bomb, finds Sonic, and fights him. It ends in a tie, neither of them win because Shadow has to escape the jungle before it blows up. So he grabs Rouge, and warps onto the ARK.
Later Eggman is on T.V everywhere and it is revealed to all he is being taped from ARK. Half of the station comes off which reveals a long pointer called the Eclipse Cannon which shots out a powerful beam, destroying half of the moon. Then, there is a timer on the screen saying 24 hours till the destruction of Earth. At the ARK, Rouge explains that she knows where the location of the last Chaos Emerald is, with Tails. Shadow and Rouge were try to catch the Tornado (Tails' plane). Rouge can't catch up in her car, and Shadow can't catch them in Sky Rail. They head back to the ARK to tell Eggman. By this time, Knuckles has unlocked the entrance to Eggman's base, so Eggman summons his Egg Golem. However, Sonic damages the head of the golem too many times, causing it to turn on Eggman. Eggman has to destroy his Egg Golem to pass. A while later, he and Shadow (who are still on the pyramid) discovers that Sonic and his friends are on the ARK. Rouge soon discovers that Knuckles is on a small planet with the pieces of the Master Emerald. She finds half of the pieces, then they fight. It is a draw and she gives the pieces to Knuckles.
Meanwhile, Eggman has kidnapped Amy Rose. A while later Eggman discovers Tails, and Sonic goes into the room he was in. Eggman shots Sonic out of an escape capsule which is going to explode, then he defeated Tails, despite his best efforts and took the real emerald. Meanwhile, Shadow, who is shocked that Sonic survived, sees Sonic run up next to him. Shadow then fights and defeats Sonic one last time. Meanwhile, Eggman is putting in the last Chaos Emerald. While he is cheering over his "victory", a screen nearby is flashing "DANGER!! DANGER!!" ( or "WARNING!! WARNING!!" in SA2:B).
It continues from the Dark Story where the cannon is flashing "DANGER!! DANGER!!" Eggman is puzzled and doesn't know what to do but then he see's his grandfather Gerald Robotnik tied to a chair on the screen of the cannon.
Meanwhile it continues from the Hero Story where Sonic and Knuckles enter the room Amy and Tails are in but then they hear a rattle and suddenly Rouge comes out of the blue. "You, you haven't give up yet?" Knuckles says. Rouge says that they are all doomed because the Space Colony Ark is heading towards Earth at a tremendous velocity. On T.V. everywhere, including the Ark, Gerald Robotnik is tied to a seat explaining how the Ark will crash into Earth and destroy it among the savage humans, with the power of all seven Chaos Emeralds.
Eggman comes in and Knuckles starts yelling at him, thinking that Eggman is behind all of this. But then Eggman gives Rouge his grandfather's diary and Rouge reads it out loud revealing that the professor went insane after his granddaughter Maria was killed. When the Space Colony ARK was shut down, Maria was killed in the process. Gerald went mad because he loved Maria so much. He wanted to curse all humans, so he made the Eclipse Cannon, and when having enough power, ergo the 7 Chaos Emeralds, would be programmed to make ARK fall to Earth. It is revealed that Gerald made Shadow for good, to benefit man-kind but Space Colony ARK was destroyed, and as a result, so was project Ultimate Life Form A.K.A. Shadow. He was able to complete his research and finish Shadow, and he says that you may awaken it "if you wish to fill the world with destruction".
The gang have to stop the energy from the Chaos Emeralds to stop the Space Colony ARK from crashing with Earth. They then have a plan to stop the Chaos Emeralds with the Master Emerald. Amy finds Shadow and convinces him to help save the world. Shadow then has a flashback of Maria telling him the same, and launching him out of a shuttle down to Earth, so he wouldn't be destroyed on the ARK. He then takes off saying "I have to go now! I need to keep my promise to Maria...and you."
Sonic and Knuckles are seen at a shrine that looks somewhat like the Shrine of the Chaos Emeralds, with the Chaos Emeralds there. When Sonic and Knuckles try to get closer to the Shrine to stop the Chaos Emeralds with the Master Emerald, Gerald's voice is heard again, and a snake/lizard like beast called the Biolizard is awakened. They realize that this is the prototype of the Ultimate Life Form, Shadow being the finished product. Shadow appears and defeats the Biolizard, while Sonic and Knuckles get to the shrine and find a space for the Master Emerald. Knuckles does the chant to negate the power of the Chaos Emeralds, and the Biolizard Chaos Controls into outer space. They hear Eggman's voice saying that the Biolizard has fused with the Space Colony ARK to become the FinalHazard and is keeping it on its crash course to Earth.
Space Colony ARK, is no longer being powered by the Chaos Emeralds, but now by the FinalHazard. Sonic and Shadow use the Chaos Emeralds to transform into Super Sonic and Super Shadow, respectively. They fight the FinalHazard in outer space, and just as they are about to stop Space Colony ARK, Maria's voice rings in Shadow's head again about giving people a chance to be happy. Both Sonic and Shadow use Chaos Control to warp the crashing space colony ARK back to its normal place, but Shadow's power is drained and he falls to Earth, realizing that he has fulfilled Maria's request in his "dying" moments.
- City Escape (Sonic)
- Mission Street (Tails)
- Route 101 (Tails)
- Aquatic Mine (Knuckles)
- Green Forest (Sonic)
- Prison Lane (Tails)
- Metal Harbor (Sonic)
- Pumpkin Hill (Knuckles)
- Wild Canyon (Knuckles)
- Hidden Base (Tails)
- Pyramid Cave (Sonic)
- Death Chamber (Knuckles)
- Meteor Herd (Knuckles)
- Eternal Engine (Tails)
- Crazy Gadget (Sonic)
- Final Rush (Sonic)
- Radical Highway (Shadow)
- Route 280 (Rouge)
- White Jungle (Shadow)
- Iron Gate (Eggman)
- Security Hall (Rouge)
- Weapons Bed (Eggman)
- Sky Rail (Shadow)
- Dry Lagoon (Rouge)
- Sand Ocean (Eggman)
- Egg Quarters (Rouge)
- Mad Space (Rouge)
- Cosmic Wall (Eggman)
- Lost Colony (Eggman)
- Final Chase (Shadow)
- Big Foot (Sonic after City Escape)
- V.S Eggman (Tails before Prison Lane)
- V.S Shadow (Sonic before Green Forest)
- King Boom Boo (Knuckles)
- Egg Golem (Sonic)
- V.S Rouge (Knuckles)
- V.S Eggman (Tails)
- V.S Shadow (Sonic)
- Hot Shot (Shadow)
- V.S Tails (Eggman after Weapons Base)
- Flying Dog (Rouge)
- V.S Sonic (Shadow after White Jungle)
- Egg Golem (Eggman)
- V.S Knuckles (Rouge)
- V.S Tails (Eggman)
- V.S Sonic (Shadow)
Levels featuring Sonic or Shadow are designed in much the same way as they were in Sonic's levels in Sonic Adventure, where the player's primary objective is simply to get to the end of the level. Levels with Tails or Dr. Eggman allow the player to control a mechanized robot walker and generally blast their way to the end, much like E-102 Gamma's stages in Sonic Adventure. Knuckles and Rouge are required to scour their levels for shards of the Master Emerald (with the exception of 2 stages where they must find keys into Eggman's base and 1 stage where Chaos Emeralds are located), again, much like Sonic Adventure. Interspersed between the levels are various bosses, which one particular character must fight. The main story line can only be finished when both "Hero" and "Dark" story modes are finished, and an extra story feature is revealed where the player must use all the characters to beat it. Within Action Stages, players collect rings and defeat enemies, with a timer counting the time spent within the level. At the end of each stage, the player is given a score based on the number or rings collected and time spent within the level. The less time is used and the more rings obtained, the higher the score is. The player is also given a rank-based performance, a letter grade that is either A, B, C, D, or E, with A being the highest and E being the lowest. Irrelevant to any other factors, an A Rank is automatically awarded to players that complete any score-ranked mission with all of the rings from that level in the player's possession. There are five missions within each Action Stage; in order to obtain the second mission, the player must complete the first one, to unlock the third, the second mission must be finished, and so on. In order from first through fifth, the missions are to complete the level, collect 100 rings, find a "lost Chao" using the Mystic Melody upgrade, finish within a time limit, and complete a "Hard mode" version of the Action Stage. Emblems are also given within the game; there are 180 Emblems in total. In order to gain all 180 Emblems, players must defeat every mission within every stage, achieve an A rank in all stages and missions, etc. After collecting all 180 Emblems, the player unlocks an extra level 3-D Green Hill level. 3-D Green Hill is a remake of Green Hill Zone from the original Sonic the Hedgehog game.
- In the trailer of the game, Sonic the Hedgehog is wearing his most popular shoes, not the Soap Shoes.
- Sonic Adventure 2 is the only game where Sonic wears Soap shoes in order to promote the product and the new extreme sport, freestyle grinding, that the shoes were made for. There are also many billboards, blimps, and benches in the game that advertised the shoes. Sonic himself wore a custom version of the Scorcher/Nitro Soap shoe, while Shadow wears a pair of custom Broadside Soap shoes, as grinding (or "soaping") debuted as an important new gameplay element.
- This is the first non spin-off game where Dr. Eggman is playable.
- Ever since grinding has been introduced in Sonic Adventure 2, almost every Sonic game after it has grinding as a core gameplay element as well.
- This is one of two games in which Eggman points a gun at someone (the other being Sonic Riders).
- In the game, Eggman blows up half of the moon, but in later games, the moon is perfectly intact. Also, the Earth doesn't appear to have any gravitational stress by the destruction of half of the moon.
- In the Dreamcast version, in the cutscene before the level City Escape, Sonic’s model has his original shoes when he escapes from the helicopter, but when he jumps off of the helicopter's wing he was somehow wearing the Soap shoes.
- All of the background music for Knuckles' stages have a sung track rather than just music (the only stage that does not have this is during Knuckles' part in Cannon's Core level). The only other levels with vocals (aside from the final boss) are City Escape, White Jungle, and Final Chase.
- In the cutscene mentioned above, the pilot of the helicopter identifies himself in military talk as "Sigma-Alpha 2", which translates from Greek as "SA2," the game's initials.
- Shadow was originally going to die in the last story, but his reception from fans caused him to be brought back for Sonic Heroes.
- There is some unused dialogue in the game, including some Omochao quotes. *Some of the deleted clips were brought back in the GameCube version, however, as an easter egg if Sonic or Shadow carries him to the goal ring.
- The G.U.N. Beetles, look very similar to the Egg Flyer enemies from Sonic the Hedgehog (2006).
- If one were to go to the Theme Select in the Options menu and rotate the Control Stick clockwise for a few moments until hearing a chime sound, they would then see a picture of the President's Secretary and should then be able to select the Secretary's Theme.
- Green Hill Zone returns as an unlockable stage, which marks its big comeback in recent Sonic games, as it had not been seen for several years. Also, the stage's background music is a remixed version of the original song, and when Sonic destroys an enemy (which are the first Badniks instead of G.U.N. robots), the same sound effects from the original game are played instead of the new sound effects.
- In the Gamecube version, when pausing, pressing and holding the Y and X buttons at the Pause Menu will make it disappear, giving the player a clear view of the screen.
- In the Mad Space level for Rouge, there are two Easter Eggs. First, go under the starting platform to its base, and kick open the iron box where you will find a blue defense item container from the Dreamcast game Phantasy Star Online: Episode I & II. Also, go to the outlying platform with a circle of rings and two iron boxes. Kick open the nearest iron box and you will see a green medical/technique item container from the same aforementioned RPG. However, neither items do anything or have any significance to the level.
- In the Chao Garden, there's a glitch that makes it possible to reuse an animal from the Action Stages multiple times on a single chao. While holding your animal, go as close to your Chao as possible without giving it the animal. Then simply drop the animal in front of your chao and, if done correctly, the chao will not only do the level up animation, but its stats will go up as if you actually handed the animal to the Chao, only now you can pick the animal up again. This can also be done with Chaos Drives and can be used to quickly raise your chao's stats. This glitch is present in both the Dreamcast and GameCube versions.
- Also in the Chao Garden, one of the shows shown on the garden's little TV (achieved by winning all Challenge Races), features a big, mustached, orange cat (Robotnik) chasing a speedy, little blue mouse (Sonic). This is a spoof of the classic cartoon show, Tom & Jerry.
- In the first cutscene of the "Last Story" when Gerald Robotnik's message was sent around the world, in the area where Eggman had one of his hidden bases and also the place where the Arabs were seen (Jerusalem or just the Middle East), in the background something that greatly resembles the holy Islamic building (mosque) called the "Dome of the Rock" can be seen.
- Tails wasn't originally planned to be in the game as a playable character but was added near the end of the game's production, which is why he's not shown in any trailers. Therefore, very few of Tails' levels had much to do with the story.
- Shadow was originally going to be named "Terios" ('reflection of'), and Rouge was going to be "Nails" (in direct contrast to Knuckles).
- In the both versions, the in-game screenshots appearing in the Tutorial and Credits are all from the Dreamcast version. While some noticeable differences such as the different-colored select button, the treasure hunting exclamation point and the controller graphic were changed, you can see there aren't any new GameCube screenshots due to some Dreamcast-only things appearing, such as the altered posters in the background of City Escape or the writing on the mechs (most clearly the Eggman insignia and "IVO" on the back vanished in the GameCube version, but it still exists in the screens). This is an oversight on the developers' part. A similar mistake occurred in Sonic Adventure DX, in which one of the buttons in one of the character instructions was that of the Dreamcast version rather than the GameCube one.
- Strangely, SA2 has three different versions of bats. The first is the anthropomorphic bat, Rouge. The second is the small animal bat, used for chao raising. And the third, is a more realistic bat, found flying in groups inside Death Chamber.
- In the Metal Harbor stage, when reaching the missile section, an announcement will alert Sonic that there is going to be a "Missile launch in 15 seconds." In the Japanese version, the announcement is the same recorded audio still in English.
- In the Dark Story, Sonic will jump and kick the Egg Golem in the head. While doing this, he says "Teriiiaaaaaa!!". In the Japanese version, Sonic says the same thing but it's longer. This could be a reference to Shadow's original name while Sonic Adventure 2 was still in development.
- In the Chao Garden, some characters will say Japanese lines (mostly Tails and Eggman). Also, the chao in the Chao Kindergarten sing songs in Japanese.
- Unlike most games, the characters go through the same locations, but at different times. For example, Shadow's Sky Rail stage is Knuckles' Pumpkin Hill stage during the day.
- In the original Dreamcast version of the game, if you insert the disk into a PC then special wallpapers will be available to download as an easter egg. As well as that, there is a list of main series Sonic Games prior to Sonic Adventure 2, although Sonic CD is absent from the list. It reads:
SERIES TITLE: SONIC the Hedgehog, 1991
SONIC the Hedgehog 2, 1992
SONIC the Hedgehog 3, 1994
SONIC and KNUCKLES, 1994
SONIC JAM, 1997
SONIC Adventure (for Japan), 1998
SONIC Adventure, 1999
SONIC Adventure International, 1999
SONIC Adventure 2 The Trial, 2000.
- In the English version, voices tend to overlap each other and cause much confusion. In the Japanese version however, the voices never overlap. This is due to the translation issues.
- In stages like Radical Highway, the billboard sign Got Milk? is promoted to say Got Ring?
- Although the Master Emerald was destroyed, neither Tikal nor Chaos were seen escaping like they did in Sonic Adventure.
- The camera can be used to move objects in the game. This is most noticeable in the Chao Garden if you have a fruit in front of the camera and the player walks away from it. The same thing can be done in the Chao Garden in Sonic Adventure.
- This is the first game in the Sonic series where any character swears. In the first cutscene of the demo version, before the player enters City Escape, the man on the radio can be heard swearing in Japanese. He says, "What the Hell?" In the final release, the English voice actor instead says, "What?!"
- This is the only game so far where Gerald Robotnik is a villain.
- Sonic Adventure 2: Battle was supposed to be released for the PlayStation 2 but it was later cancelled.
- This is also one of the only two games that features the Space Colony ARK, the other one being Shadow the Hedgehog.
- In the City Escape level, there is a scene where Sonic is being chased by a G.U.N. truck, similar to how Sonic was chased by an orca in the Emerald Coast level in Sonic Adventure.
- In the cutscenes featuring space on both Sonic Colors and Sonic Unleashed, the Space Colony ARK was not shown.
- There are cameo appearances in several Chao. The Sonic and Shadow Chao are easily obtained, as well as a NiGHTS and Reala (from NiGHTS) one. However, there are special Tails, Amy, and Knuckles Chao as well.
- Some of the characters' theme songs are based on their Sonic Adventure songs, most notably Sonic and Tails', and Amy's theme song is exactly the same.
- This game's port is the first Sonic game for a Nintendo home console.
- Shadow has the least amount of stages out of all the characters, with only 4 (Radical Highway, Sky Rail, White Jungle, and Final Chase).
- The "Chao in Space 2" movie billboard as well as the billboard advertising for the DVD Edition of "Chao in Space" in City Escape refers to the "Chao in Space" movie billboard near the entrance of Casinopolis in Sonic Adventure.
- In the Dreamcast version of the game it had Big in multiplayer battle mode he rode in Eggman's Walker, but was replaced by Dark Chao Walker in the Gamecube remake.
- In Sonic Generations, Shadow is Sonic's rival, during the Opening Cutscene, it is a Reference to the Sonic Adventure 2 Battle Opening, and during the fight, A Remix of For True Story plays, and if Sonic grabs Two or Three Power Cores depending on the difficulty, Live and Learn plays for a brief time.
- City Escape returns in Sonic Generations, as the fifth level in the game, in the Dreamcast Era.
- Radical Highway returns in the 3DS version of Sonic Generations.
- You have the option to play Metal Harbor and Green Forest as backround music in Sonic Generations.
- In the Hub World in Sonic Generations, when in Dr. Eggman's section of the hub, A Remix of E.G.G.M.A.N plays.