Let's just say that every single existing player can invoke one by FC (Full Combo)-ing an insanely hard (or long) beatmap, or dethroning top players at certain beatmaps. Passing a "thought-to-be-humanly-impossible" map also counts.
Cookiezi is basically the source of almost all awesome moments that happened in this game. Examples:
He got to 1,025x combo on "The Big Black", generally regarded to be one of the hardest beatmap the community has ever seen.
Almost FC'd "chipscape", which is another extremely hard beatmap known to players, with the HD (Hidden) mod.
FC'd "Symphonic Love" on the Love difficulty with the DT (DoubleTime), HD, AND FL (Flashlight) mods. It's not the beatmap that is crazy, it's basically THIS guy that's going frantic.
And then he got to FC "Sayonara Kimi no Koe" on Insane, with the exact same mods as when he FC'd "Symphonic Love". And then he quitted. Sayonara, indeed.