Boss Time Attack mode Successfully complete the story mode on either hero or dark mode to unlock  this mode.  Complete Hero story to fight all the bosses in that story.  Complete Dark mode to fight all the bosses in that story. 

Access the hidden Island level  Get all 180 emblems.  This new level is a 3D version of the "Green Hills" zone from the original "Sonic the Hedgehog".

 Get Extra Costumes  Get A ranks on every mission with the character you want the costume for.