Get a 100% completion for Sonic, Shadow, or Silver's episode to unlock the Audio and Theater room under the Extras menu.

Successfully complete Sonic, Shadow, and Silver's episode to unlock the Last episode.

Get an "S" rank on all of Sonic, Shadow, and Silver's levels, Bosses, and town missions to unlock Free mode.

Successfully complete Crisis City with Sonic to unlock Shadow's episode.

Successfully complete the Silver The Hedgehog Boss battle with Sonic to unlock Silver's episode.

Successfully complete the indicated task to unlock the corresponding character in Free mode:

Amy Rose: Successfully complete all Soleana mystery missions with an "S" rank.
Blaze the Cat: Successfully complete all Soleana mystery missions.
E-123 Omega: Successfully complete all GUN Commander missions with an "S" rank.
Knuckles the Echidna: Successfully complete all Town Stage missions with an "S" rank.
Miles "Tails" Prower: Successfully complete all Town Stage missions.
Rouge the Bat: Successfully complete all GUN Commander missions.

Successfully complete the indicated episode with a 100% rank to unlock the corresponding theme in the Audio Room:

Elise's Theme: The Last Episode
Shadow's Theme (All Hail Shadow): Shadow's Episode
Silver's Theme (Dreams of An Absolution): Silver's Episode
Sonic's Theme (His World): Sonic's Episode

In Multiplayer mode in any level or match, equip the Red Gem on Sonic, activate it and hold it, then die. While still holding the activation button, wait until you respawn. When you respawn, deactivate the gem. You will now run much faster than normal and the time will automatically be slow.

Jump with Silver by pressing X, then press X again while in mid-air. This makes Silver float around. When floating in mid-air, tap X while moving in any direction instead of holding the button down to make Silver jump further.

When facing an enemy that requires more than one hit, use your Homing Attack on it then use your Bounce Attack. Note: You must first have the Bounce Bracelet.

When you fight Silver with Sonic, first do a slide move into him as he is falling from the sky. Then, collect a ring and run around until you hear "How bout this?", then do a homing attack on him. Run away again until you hear "How bout this?" again. then do a homing attack again. Repeat this until he is defeated.

First, use Silver to weaken him until his first arm guard falls off. Then, switch to Shadow and hit him with the beams until his second arm guard falls off. Next, use Sonic to defeat the rest of his first form. Finally, use all three to survive the blows of lasers, and continuously attack.

While playing the game, press Up to display Niko's cell phone. Press Up again to access the keypad. Then, enter one of the following codes to activate the corresponding cheat function. Once a code has been entered correctly, a new "Cheats" menu option will be available on your phone, below "Options", where you can access the cheats without having to enter the phone number again. Note: Do not save the game after enabling a code to avoid unforeseen problems. You can usually only spawn one vehicle at a time. Any previously spawned vehicles will disappear. However, if you spawn a vehicle, save the game, and load again, you can spawn another one and your original will not disappear. You must have it in your parking space in front of a safehouse or it will be gone before you have a chance to spawn another.

Full health and armor

Dial "3625550100" on the cell phone. If you enter this code while in a vehicle, it will also repair it. Note: This phone number translates to "DOC-555-0100".

Full health, armor, and ammunition

Dial "4825550100" on the cell phone. If you enter this code while in a vehicle, it will also repair it. Note: This phone number translates to "GTA-555-0100".

Weapons tier 1

Dial "4865550100" on the cell phone. This will unlock the baseball bat, handgun, shotgun, MP5, M4, sniper rifle, RPG, and grenades. Note: This phone number translates to "GUN-555-0150".

Weapons tier 2

Dial "4865550150" on the cell phone. This will unlock the knife, Molotov cocktails, handgun, shotgun, Uzi, AK47, sniper rifle, and RPG. Note: This phone number translates to "GUN-555-0100".

Remove Niko's wanted level

Dial "2675550100" on the cell phone. Note: This phone number translates to "COP-555-0100".

Add one star to Niko's wanted level

Dial "2675550150" on the cell phone. Note: This phone number translates to "COP-555-0150".

Spawn Annihilator police helicopter

Dial "3595550100" on the cell phone. The Annihilator is armed with rockets. Note: This phone number translates to "FLY-555-0100".

Spawn Cognoscenti

Dial "2275550142" on the cell phone. Note: This phone number translates to "CAR-555-0142".

Spawn Comet

Dial "2275550175" on the cell phone. Note: This phone number translates to "CAR-555-0175".

Spawn FBI Buffalo

Dial "2275550100" on the cell phone. Note: This phone number translates to "CAR-555-0100".

Spawn Jetmax

Dial "9385550100" on the cell phone. Note: This phone number translates to "WET-555-0100".

Spawn NRG-900

Dial "6255550100" on the cell phone. Note: This phone number translates to "MBK-555-0100".

Spawn Sanchez

Dial "6255550150" on the cell phone. Note: This phone number translates to "MBK-555-0150".

Spawn SuperGT

Dial "2275550168" on the cell phone. Note: This phone number translates to "CAR-555-0168".

Spawn Turismo

Dial "2275550147" on the cell phone. Note: This phone number translates to "CAR-555-0147".

Change weather and brightness

Dial "4685550100" on the cell phone. Note: This phone number translates to "HOT-555-0100".

Go to a TW@ Internet Cafe, log into a computer, and enter "www.whattheydonotwantyoutoknow.com" as a URL to view maps that reveal all weapon, health, armor, vehicle, pigeon, ramp/stunt, and entertainment locations.

Successfully complete the indicated task to unlock the corresponding bonus:

Annihilator police helicopter: Collect all 200 pigeons (flying rats).

No ammo limit: Get a 100% completion.

Rastah Color Huntley SUV: Successfully complete 10 Package Delivery missions.

Reach the indicated level of friendship with the corresponding character to unlock their special friendship ability:

Alex (screen name "LiberatedWoman")

Method: Look for the personal ad from "LiberatedWoman" in the "Women seeking men" section of the "www.craplist.net" website. Alex is somewhat of a self-centered, spoiled rotten rich girl. She will compliment Niko for wearing expensive clothing and driving expensive cars. She will also write about her exploits with Niko in her blog at "www.blogsnobs.org". Reach 80% friendship with her.

Special ability: 50% off at all clothing stores.

Brucie

Method: Take him bowling, drinking, eating, strip clubs, shows, helicopter tours, and boating to reach 70% friendship.

Special ability (Chopper Ride): Call Brucie, and he will fly his helicopter to you. This allows you to fast travel to various portions of the city.

Carmen (screen name "SoboHoe")

Special ability (Health Boost): Restores Niko's health over the phone. She will call Niko every chance she gets.

Dwayne

Method: Take him to strip clubs, eating, drinking, shows, and bowling to reach 60% friendship.

Special ability (Extra Help): Call Dwayne to have a car full of gang members follow you.

Kiki (screen name "LawChick")

Method: Date LawChick via "www.love-meet.net" through the in-game internet. Take her out a few times to reach 75% friendship. When dropping her off, select the "Try your luck" option. Afterwards, she will call you and say she can clear the feds.

Special ability (Remove Up to 3 Wanted Stars): Call her on your cell phone, and select "Clear wanted levels".

Little Jacob

Method: Take him to darts, shows, pool, drinking, eating, and strip clubs to reach 60% friendship.

Special ability (Discount Guns): Call Little Jacob, and he will drive out a car full of guns for you to buy.

Packie