These advantages can be unlocked ether in the extras menu, time attack or playable characters.

Extra	How to unlock
D.A. Garden	Clear time attack mode with a combined total of 25 minutes. Or complete the game with all time stones.
Play as tails	Beat the game once.
Sound test	Clear special zone time attack with a combined total of 4 minutes or under.
Special stage time attack	Beat every level (including bosses) in normal time attack mode.
Stage select	Clear special zone time attack with a combined total of 5 minutes or under.
Visual mode	Clear time attack mode with a combined total of 25 minutes or under.