Sonic Series || Geometry Dash
Review of all of the official sonic series levels: Supersonic, Ultrasonic (insane demons) , Hypersonic and Subsonic (extreme demons)
Levels like Panasonic, Electrosonic and Electrolux are not included, because they were not made by the original team.
None of the levels are on the demon list, but all of them have been back in the day.