Treasure Hunter
Collected all the Chaos Emeralds.
There are 7 to collect. (obviously, if you've played any other Sonic)
3 you get from Rival Battles:
Metal Sonic:
Shadow:
and Silver:
3 are from Boss Battles:
Death Egg Robot:
Perfect Chaos:
and Egg Dragoon:
And 1 of the Emeralds is collected in a cutscene after restoring Planet Wisp.