For me, this is one of the most insightful of your many insightful posts. The only things I might add are (1) that the nemesis is often not only the protagonist’s shadow side but the writer’s shadow as well, which may be one reason that antagonists in scripts by developing writers are simple bad guys, and (2) that the nemesis is often the catalyst for protagonist to break out of stasis (as you’ve commented before), and thus the nemesis represents the protagonist’s reluctant awareness of the need for change, i.e. integration, an awareness that the protagonist initially resists by designating the nemesis / antagonist as the other rather than the submerged side of the protagonist her/himself. Your examples illustrate these concepts beautifully.

As Nabokov said about R. L. Stevenson’s “Dr. Jekyll and Mr. Hyde,” the main point is that Jekyll and Hyde are one person, not two.” By the way, Stevenson was preoccupied with the shadow and the unconscious or what Freud would call the id, even in his children’s poetry, a decade before Freud and Jung.