I will attempt to explain what affects the "cool score" that you get at the end of each act. I will also add my 2 cents on how this could have been done better.
How Does It Work?
Cool score is the newest addition of bonus points and it's added at the end of each act based on your performance.
But what affects the amount of points that you'll get?
At the beginning of each stage your cool score is already at 10000 points. Yep, that's right! Every act assumes perfect cool score. That score, however, gets reduced every time you get hit.
I haven't tested whether losing a life reduces it more than say losing just your rings are yet to be tested. However, I've tested the following:
- Using the restart option from the pause menu: Restarting the act this way carries your cool score over. Say you got hit once and you decided to restart the stage. Your cool score now is assumed to be 9000 no matter whether you'll get hit during this run or not.
- Restart a world through the save select menu: Restarting this way is obviously worse since if you were in act 2 of any world you're stuck on going back to act 1. However, this is the only method to reset your cool score back to 10k.
Cool! Does this Mean that Score is Better as a Metric of Performance or Whatever?
As long as you can sacrifice lives to farm score over and over, and as long. as you can just restart any act carrying your score over and over again, score implementation in Sonic games has a long way to go (or even don't go anywhere and get scrapped entirely).
With that said you can still feel good for hitting that sweet 10k at the end of every act because there's a difference between the player who gets hit a dozen times and the player who flawlessly breezes through every level.
In other words, the scoring system of Sonic Mania is a step towards the right direction of measuring performance but not quite there. Another genre that still uses scoring for this use is shmups but for shmups you rarely have to start over the stage, and using a continue resets your score back to zero. There's rarely a "scummy" method of accumulating a high score.
I hope that I helped you understand what cool score is.