The main ladder
Geometry Dash rates levels with a ladder of faces, and each step up adds a specific kind of demand rather than just "more of the same". Easy assumes you can jump and fly a spacious ship corridor. Normal chains timings steadily. Hard introduces gravity portals and tighter corridors. Harder mixes speed changes and dual-mode sections. Insane compresses everything - tight wave lanes, frame-strict timings, sections where the camera itself works against you. The official main levels sample this ladder one tier at a time, which is why beating the campaign's later levels is the standard warm-up before demon hunting.