In just about all of the stages you have three choices: to help the Dark side, yourself, or the Hero side whenever you have someone with you and it is not a Boss fight. To change the character you want with you, press Start. There will most likely be three selections: Dark, Neutral, and Hero. Press Left or Right to highlight a character or ring in the middle. Press A to select the highlighted character. That character will remain with you until your next run in with the other character. You can then simply press Start and do the process again. You cannot select a Hero partner if there is an 'X' over the Hero side. You cannot select a Dark partner if there is an 'X' over the Dark side.
Another way to do this is to use the D-Pad on the controller during the game. Press Right for the Hero character, Left for the Dark character, and Down for the Neutral character.
Chosen One Song
Successfully complete the Semi Hero story line.
Death Ruins: Black Bull
Do not bother using the homing attack; it is too hard to get to, and it is difficult to keep hitting him like that. Instead, defeat the two Black Arms soldiers and collect the guns from them. Then, head for the spring and use it. Move forward a bit so you do not start grinding the rails. Pass Black Bull in your jump, and rapidly shoot a little before you level with its eye. Repeat the strategy, and if you fill your Hero gauge, activate Chaos Control and finish him off. This seems easier than to grind around him and shooting him every time around, which wastes ammunition on a lot of missed shots.
Defeating Black Bull
Use the following trick to defeat Black Bull in Death Ruins. Kill lots of soldiers. Then after getting the desired number of bullets, shoot him. When you get Chaos Control, use it and shoot him rapidly. The shots will keep the Hero meter full and you will kill him.
Defeating Devil Doom
Play as Super Shadow and hit him with the Chaos Spear(s). First, try to avoid the meteors that shoot lasers at you, or destroy them if desired. Charge your Chaos Spear with Square and blast Devil Doom in the eye. Devil Doom's third eye will go to the other head. Go to the other side and charge your Chaos Spear. Blast him in the eye again. Note: Make sure to shoot the balloons to get rings if you are running low. When you blast him in the eye immediately, go to the other side, and charge your blast . When Devil Doom's third eye gets to the other side of the head, blast him. Go to the other side and blast him, then go to the other side blast him and repeat.
Egg Vacuum
Successfully complete the Neutral story line with the Hero ending. Use the Egg Vacuum to suck up 20 objects to gain an extra life.
Expert Mode
Get 'A' ranks in all stages in the game.
Extra ammunition
Go to the stage were you have to kill the Chaos. There is a room near two GUN soldiers and a Chaos that has two weapon boxes in it. Break both boxes, then go in the room with the GUN soldiers. Go back and the boxes will be back. You can repeat this as many times as desired.
Heal Cannon
Successfully complete the Hero story line.
Hyper Shadow
In order to turn into Hyper Shadow you first need to complete all the endings for all the stories. This includes the good and evil storylines. Once you do this, you will unlock the Last Story. Choose the Last Story and you will begin a level called The Last Way after some intermission sequences. Once you complete this and reach Black Doom, there will be an intermission sequence, at the end of which Shadow takes the Chaos Emeralds and turns into Hyper Shadow.
To defeat Devil Doom as Hyper Shadow, hold Square to charge Chaos Spear and hit it numerous times. Get lots of rings and you will survive.
Key bonuses
Collect all five hidden keys in the indicated level to unlock the corresponding bonus behind the five-keyed doors.
Effect - Code
2 Turrets - Get all 5 keys in Black Comet
3 Extra lives - Get all 5 keys in The ARK
Alternate path to a red terminal - Get all 5 keys in Mad Matrix
Armored Car - Get all 5 keys in Lost Impact
Black Hawk - Get all 5 keys in Glyphic Canyon
Black Volt - Get all 5 keys in Sky Troops
Extra shooting gallery - Get all 5 keys in Circus Park
Large GUN Cannon - Get all 5 keys in Lethal Highway
Opens cage, which triggers shortcut to the end of the level - Get all 5 keys in The Doom
Shortcut - Get all 5 keys in Cryptic Castle
Switch that makes ring trails to the end of the level - Get all 5 keys in Cosmic Fall
Turrets - Get all 5 keys in Final Haunt
Warp Hole - Get all 5 keys in Death Ruins
Warp Hole - Get all 5 keys in Space Gadget
Warp Portal - Get all 5 keys in The Last Way
Last Story
Successfully complete every sixth stage in story mode, defeat all Bosses at the end (all five Hero and all five Dark Bosses), and see all ten Hero and Dark story line endings.
Level 2 Weapons
Successfully complete both the Hero and Dark versions of a story line.
Library Sequences
Complete the indicated path of story mode missions to unlock the corresponding intermission sequences at the Library:
1: Punisment, Thy Name Is Ruin: Dark, Dark, Dark, Dark, Dark, Dark, Dark final Boss
2: Prologue To World Conquest: Dark, Dark, Dark, Dark, Dark, Dark, Hero ending
3: The March To A Darker World: Dark, Neutral, Dark, Neutral, Hero, Dark
5: Purification Via Ruination: Dark, Dark, Dark, Hero, Dark, Dark ending
6: Apogee Of Darkness: Dark, Dark, Dark, Hero, Dark, Hero ending
7: True Soldier Of Destruction: Dark, Dark, Dark, Hero, Neutral, Dark ending
8: Believe In Yourself: Dark, Dark, Dark, Hero, Neutral, Hero
11: Revenge At Last: Dark, Dark, Neutral, Dark, Dark, Dark ending
15: The Nightmare's Insulation: Dark, Dark, Neutral, Neutral, Dark, Dark ending
16: The Nightmare's Sublimation: Dark, Neutral, Neutral, Neutral, Dark, Hero
17: The Loner's Choice: Dark, Dark, Neutral, Neutral, Neutral, Dark
18: Subjugation IN BLACK: Dark, Neutral, Neutral, Neutral, Neutral, Neutral
27: The Cleansing of Darkness: Dark, Dark, Hero, Dark, Dark, Dark
45: The World's Demise: Dark, Hero, Dark, Dark, Dark, Dark ending
48: Vainglory or Abandonment?: Dark, Hero, Dark, Dark, Neutral, Hero ending
51: Controller from the Capsule: dark, hero, dark, neutral, neutral, dark
52: Beyond One's Own Power...: Dark, Hero. Dark, Neutral, Neutral, Good.
57: Transcendentalism: Dark, Hero, Dark, Hero, Neutral, Dark.
78: Power Of Love: Dark, Hero, Neutral, Hero, Hero, Hero
80: Walk My Way: Dark, Hero, Hero, Dark, Dark, Hero ending
91: The Rise and Fall Of The ARK: Dark, Hero, Hero, Hero, Dark, Dark
98: Severed Chains: Neutral, Dark, Dark, Dark, Hero, Hero.
102: Arriving At The Ego: Neutral, Dark, Dark, Hero, Neutral, Hero ending
105: Demise Wrought by Tragedy: Neutral, Dark, Neutral, Dark, Dark, Dark
111: Soldier Of Grief: Neutral, Dark, Neutral, Neutral, Neutral, Dark ending
112: Reclaimed Heart: Neutral, Dark, Neutral, Neutral, Neutral, Hero
120: Spawn Of The Devil: Neutral, Dark, Dark, Hero, Hero, Hero ending
121: Black Doom's Scheme: Neutral, Dark, Hero, Dark, Dark, Dark ending
135: A Vow For The Victims: Neutral, Dark, Hero, Hero, Neutral, Dark
144: One To Succeed A God: Neutral, Neutral, Dark, Neutral, Dark, Hero ending
145: Disappointed In Humanity: Neutral, Neutral, Dark, Neutral, Neutral, Dark
146: Faith Taken From Solitude: Neutral, Neutral, Dark, Neutral, Neutral, Neutral, Hero final Boss
153: Together With Maria...: Neutral, Neutral, Dark, Hero, Hero, Dark ending
154: The Tragedy's Conclusion: Neutral, Neutral, Neutral, Dark, Hero, Hero, Hero ending
155: The Day That Hope Died: Neutral,Neutral,Neutral, Dark, Dark, Dark
159: At Least, Be Like Shadow...: Neutral, Neutral, Neutral, Dark, Hero, Dark
160: Seeking A Silent Paradise: Neutral, Neutral, Neutral, Dark, Hero, Hero
161: The Lion's Awakening: Neutral,Neutral,Neutral,Neutral, Dark, Dark ending
162: Identity: Neutral, Neutral, Neutral, Neutral, Dark, Hero ending
163: An Android's Rebellion: Neutral, Neutral, Neutral, Neutral, Neutral, Dark
164: A New Empire's Begining: Neutral, Neutral, Neutral, Neutral, Neutral, Neutral, Hero final Boss
165: Bullets From Tears: Neutral, Neutral, Neutral, Neutral, Hero, Dark ending
166: Journey To Nihility: Neutral, Neutral, Neutral, Neutral, Hero, Hero
168: Dr. Eggman's Miscalculation: Neutral, Neutral, Neutral, Hero, Dark, Hero
170: Requiem For The Heavens: Neutral, Neutral, Neutral, Hero, Neutral, Hero ending
171: Sonic Dethroned: Neutral, Neutral, Neutral, Hero, Hero, Dark
175: Farewell To The Past: Neutral, Neutral, Hero, Dark, Neutral, Dark ending
182: Compensation For A Miracle: Neutral, Neutral, Hero, Neutral, Neutral, Neutral, Hero final Boss
191: Dark Soldier: Neutral, Hero, Dark, Dark, Neutral, Dark.
195: Birth Of The Dark Soldier: Neutral, Hero, Dark, Neutral, Dark, Dark
203: Perpetual Voyage: Neutral, Hero, Dark, Hero, Neutral, Dark
215: Wandering For Eternity: Neutral, Hero, Neutral, Neutral, Neutral, Dark ending
216: At Vagrancy's End: Neutral, Hero, Neutral, Neutral, Neutral, Hero ending
220: The Importance of Truth: Neutral, Hero, Neutral, Hero, Neutral, Hero ending
225: Solitary Journey: Neutral, Hero, Hero, Dark, Neutral, Dark.
228: I Shall Be The One To Judge: Neutral, Hero, Hero, Dark, Hero, Hero ending
229: Gone With The Darkness: Neutral, Hero, Hero, Neutral, Neutral, Dark
230: The Ultimate Choice: Neutral, Hero, Hero, Neutral, Dark, Hero
231: I Am The Strongest!: Neutral, Hero, Hero, Hero, Hero, Dark ending
232: Justice's Awakening: Neutral, Hero, Hero, Hero, Hero, Hero ending
259: A Heart Bound To The ARK: Hero, Dark, Neutral, Neutral, Hero, Dark ending
262: Steel Combat Boots: Hero, Dark, Neutral, Hero, Dark, Dark ending
263: Protector Of The Ashen Moon: Hero, Dark, Neutral, Hero, Neutral, Dark ending
266: I Know The Will Of Heaven: Hero, Dark, Neutral, Hero, Hero
275: The Reason You Were Born: Hero, Dark, Hero Neutral, Neutral, Dark
276: The Dark Part Of The Galaxy: Hero, Dark, Hero, Neutral, Neutral, Hero.
282: Beloved Memories: Hero, Dark, Hero, Hero, Hero, Hero
283: Birth Of A Devil: Hero, Hero, Dark, Dark, Dark, Dark
291: The Doctor's Lie: Hero, Hero, Dark, Neutral, Neutral, Dark
309: Funeral Procession In Space: Hero, Hero, Neutral, Neutral, Neutral, Dark
316: The One Who Maria Entrusted: Hero, Hero, Hero, Neutral, Hero, Hero
317: A.1's Enlightenment: Hero, Hero, Hero, Hero, Neutral, Dark, Dark ending
318: A Dying Empire's Cry: Hero, Hero, Hero, Dark, Dark, Hero
320: Tear-Soaked Hometown: Hero, Hero, Hero, Dark, Neutral, Hero ending.
321: Sparks On The Horizon: Hero, Hero, Hero, Dark, Hero, Dark ending
322: A Use For A Saved Life: Dark, Neutral, Dark, Hero, Dark
323: Coffin Of Memories: Hero, Neutral, Hero, Neutral, Dark, Dark
324: The Self-Imposed Seal: Hero, Hero, Hero, Hero, Neutral, Hero
325: Pretense in the Mirror: Hero, Hero, Hero, Hero, Hero, Dark
326: A Missive From 50 Years Ago: Hero, Hero, Hero, Hero, Hero, Hero, Hero final Boss
Never Turn Back Song
Successfully complete the Dark story line.
Omochao Gun
Successfully complete the Semi Hero story line.
Renegade as name
Do fifteen Dark missions and two Hero missions. When Eggman or Doom's Eye speaks to you, will be refereed to as ''Renegade".
Samurai Blade
Successfully complete the Dark story line.
Satellite Laser
Successfully complete the Semi Dark story line.
Save lives in Expert mode
When playing in Expert mode, you must go through all of the levels one at a time without a break or mission, and on a harder difficulty. You are given five lives, any lives you pick up, but cannot continue. If you lose all your lives, you must start all the way back on the first level. However, if you find yourself in a dangerous position (for example, falling off a cliff), press Start before the game registers the loss of the life, then select "Quit". At the Expert mode menu, select "Resume". At the cost of starting at the beginning of the level you were on, you will not lose that life and resume with whatever total you had previously.
Shadow Rifle
Successfully complete the Last Story.
Songs
Complete the indicated task to unlock the corresponding song.
Air Fleet Theme: Play the Air Fleet level.
All Of Me: Successfully complete the Last Story.
All Hail Shadow: Successfully complete the Hero story line.
Almost Dead: Successfully complete the Dark story line.
Black Bull Boss Theme: Defeat Black Bull.
Black Comet Theme: Play the Black Comet level.
Black Doom Boss Theme: Defeat Black Doom.
Central City Theme: Play the Central City level.
Chosen One: Successfully complete the Semi Hero story line.
Circus Park Theme: Play the Circus Park level.
Cosmic Fall Theme: Play the Cosmic Fall level.
Cryptic Castle Theme: Play the Cryptic Castle level.
Death Ruins Theme: Play the Death Ruins level.
Devil Doom Boss Theme: Defeat Devil Doom.
Diablon and Sonic Boss Theme: Defeat those Bosses.
Digital Circuit Theme: Play the Digital Circuit level.
Egg Breaker Boss Theme: Defeat Egg Breaker.
Egg Dealer Theme: Defeat Egg Dealer in the Neutral story line.
Ending: Defeat Devil Doom.
Event 1 Theme: Listen to the Event 1 Theme in story mode.
Event 2 Theme: Listen to the Event 2 Theme in story mode.
Event 3 Theme: Listen to the Event 3 Theme in story mode.
Event 4 Theme: Listen to the Event 4 Theme in story mode.
Final Haunt Theme: Play the Final Haunt level.
Glyphic Cannon Theme: Play the Glyphic Cannon level.
Gun Fortress Theme: Play the Gun Fortress level.
Heavy Dog/Blue Falcon Remixed Boss Theme: Defeat those Bosses.
Iron Jungle Theme: Play the Iron Jungle level.
Lava Shelter Theme: Play the Lava Shelter level.
Lethal Highway Theme: Play the Lethal Highway level.
Lost Impact Theme: Play the Lost Impact level.
Mad Matrix Theme: Play the Mad Matrix level.
Never Turn Back: Complete the Last Story in the Dark story line.
Prison Island Theme: Play the Prison Island level.
Sky Troops Theme: Play the Sky Troops level.
Space Gadget Theme: Play the Space Gadget level.
The Ark Theme: Play The Ark level.
The Doom Theme: Play The Doom level.
The Final Way: Play The Final Way level.
Waking Up: Complete the Neutral story line.
Westopolis Theme: Play the Westopolis level.
Two Player Mode
Use controller two to play as the Hero characters, such as Sonic, Tails, Knuckles, etc. This does not work with Doom's Eye. It also works with Maria. They cannot pick up guns.
Yuji Naka Reference
Sometimes the GUN soldiers will say odd things. One of the things that they say is 'Mr. Yuji Naka is all right.' Yuji Naka is the creator of the Sonic series.