To play a different character in Kart mode you have to first complete the required stages and missions of that character to unlock them.

Play as Sonic in PSO Suit:
Complete ALL of Sonic's stages and missions in Kart mode.

Play as Shadow in Alternate Costume:
Complete ALL of Shadow's stages and missions in kart mode.

Play as Rouge in Alternate Costume:
Complete ALL of Rouge's stages and missions in kart mode.

Play as Eggman in Alternate Eggwalker:
Complete ALL of Eggman's stages and missions in kart mode.

Play as Tails in the Tornado 1:
Complete ALL of Tails' stages and missions in kart mode.

Play as Knuckles in Alternate Form:
Complete ALL of Knuckles' stages and missions in kart mode.

Play as Amy Rose in Kart Mode:
Complete ALL of Sonic's stages and missions with an 'A' ranking in kart mode.

Play as Metal Sonic in Kart Mode:
Complete ALL of Shadow's stages and missions with an 'A' ranking in kart mode.

Play as Tikal the Echinda in Kart Mode:
Complete ALL of Knuckles' stages and missions with an 'A' ranking in kart mode.

Unlockable Items:
Win the following levels to unlock the corresponding items in the game.

Unlock Ball for Dark Garden:
Win the first 2 levels of the Dark race.

Unlock Ball for Hero Garden:
Win the first 2 levels of the Hero race.

Unlock Watering Can:
Win ALL 3 levels of the Stump Valley race.

Unlock Car:
Win ALL 3 levels of the Mushroom Forest race.

Unlock Rattle:
Win ALL 3 levels of the Block Cannyon Race.

Unlock Shovel:
Win ALL 3 levels of the Crab Pool race.

Unlock Radio for Dark Garden:
Win ALL 4 Dark Races.

Unlock Rocking Horse for Hero Garden:
Win ALL 4 Hero Races.

Unlock Ball for Normal Garden:
Win the first 4 levels of the Challenge race.

Unlock Broom:
Win ALL 5 levels of the Topaz race.

Unlock Sonic Cudly Toy:
Win ALL 5 levels of the Aquamarine race.

Unlock Note in a Bottle:
Win ALL 5 levels of the Dimond race.

Unlock Pencil Case:
Win ALL 5 levels of the Onyx race.

Unlock Picture Book:
Win ALL 5 levels of the Perridot race.

Unlock Pogo Stick:
Win ALL 5 levels of the Garnet race.

Unlock Jack in the Box for Normal Garden:
Win the first 8 challenge races.

Unlock Chao TV:
Win ALL 12 Challenge Races.


Unlock Green Meadow Stage:
Successfully beat ALL Sonic's missions with an 'A' rank to unlock 'Green Meadow' stage which was the very first sonic stage from the arcade version. Green Meadow Stage will have Sonic 2's graphics.

Unlock Boss Attack Mode:
Complete either Hero or Dark side story modes to unlock the Boss Attack
mode. Fight each Boss from either Hero or Dark side.

Last Stage:
Complete the Hero and Dark side story modes successfully then enter Story mode and a Last Stage? selection will appear on the menu between the Hero and Dark selections.