Uh, G.E.R., I think you left out mapping all the Challenge Missions that are unlocked after finishing each Act in all 6 main Stages, and then the last by finishing all 2 unlocked Missions from "Sonic Colors DS".
Those Missions, while serving as the game's side content are, yes, slightly modified layouts of already existing Acts with blockades with different objectives, but they do offer some replay value.
And, as you may or may not remember, there are 2 Red Star Rings found in each Mission, alongside the 5 in each Act.
Just thought I'd let you know.
