From the Option menu, you can change the shape of the Puyos used in most single and multi-player matches. You start with 3 styles (Real, Classic, and Fever) but you can unlock more through story mode by finishing each character's story with an overall S-rank. A special shape is also unlocked through training mode.

Effect - Code

Betanuri - 10 S-ranks
Chalk - Clear all 300 drills in training
Clear - 22 S-ranks
Cube - 15 S-ranks
Moji - 5 S-ranks