Achievement: A Quick Breather
To get this Achievement you will need to obtain the Red Ring Star located in Rooftop RUN 2. Make sure to pick modern sonic for this one.
The Red Ring will be located at the last section of the level. The exact location is on the far right, right before the final jump that takes you to the end of the level.
I have also included a video to show you the red ring. I take no credit for this video, it comes from the user Aura313Productions!
Hope this helps