Concentration: There are almost no levels that use Cheshyre and Lothyde songs, and they're really cool (and I think this while listening to them). Plus, they're on NG, so no need to go through any NONG shenanigans. Their slow pace is great for 0.5x speed levels or platformer levels, so I'll build a half speed level around their song and come up with smaller ideas on the fly.
Brainstorming: Bold of you to assume I have friends who play GD regularly. I'll assume that I'm making some 2p level and think to myself: "Hm... how can I improve the sync/song rep in this level? That's easy. I'll have one side that focuses on certain instruments and another side the focuses on another set of instruments."
SCAMPER: Rearrange: Most 2p levels have the two players separated from each other with a barrier or other method. Think codep, wobbling machine, multition, etc.. But what if instead of separating the icons, they were able to go anywhere and were not restricted to a certain part of the screen?
Ramsey Method: Stars have lives. They start out as a cloud of gas, then a protostar forms, then it reaches its T-tauri phase and when its core is hot enough, starts nuclear fusion. When the hydrogen fuel runs out, it starts becoming a red giant. It starts to fuse heavier elements such as helium and carbon, and once it reaches iron, the core collapses because of how much energy it takes. For large stars, it can implode into a neutron star or a black hole. https://byjus.com/physics/life-cycle-of-stars/
So for the level, why not make it centered around the lifetime of a star? It starts out as gas, then it goes through the phases, and when the drop hits, we see that it has run out of hydrogen fuel and starts fusing other elements. Then, at the end, it fuses iron, and the core collapses, causing the star to implode into a black hole, swallowing the player and the screen. i cooked ngl