Re: Cthulhu question in FL
Don't understand the question, i think, so here's my try of an explanation:
Cthulu works with chords in two ways, either triggering pre-programmed chords by single key strokes or interpreting midi input chords (for the arpeggiator, when the "chords" mode is inactive). The former is just various chords mapped to keys, easy compositions without breaking your fingers, the latter analyzes the input chord and puts out the most likely key (some chords fit into various scales).
The section you reference in the tutorial video is just showing the recording of cthulhus output chords via i/o mapping. You can use these notes (sustained) as input for the arpeggiator again as well, create endless working combinations of layers of layers of sounds.
Best way imho is to work out something simple and edit the recorded result to add mood/complexity.