Another one started at work.  I still had Desdemona fresh in my mind when I came up with the first couplet, which is very similar in structure.  From there, I started thinking something like Nightmare on Elm St. and Freddy Kreuger, which by the way, I couldn't even finish watching because it was just so unappealing (to me).  So I started winding through all the imagery of a shade demonizing my dreams, and I realized pretty soon I'd need to take it somewhere or else it would just be Nightmare in poem form.  So I pulled out my list of titles (again), and looked for one that seemed appropriate, and I hit on one not long after, Nuisance.  So thinking to myself, I wondered what it would be like if this nuisance, as obviously this shade would be, were not the true nuisance of the poem, but was a nuisance meant to eliminate another larger nuisance- the mongoose to a snake, for instance.  And that's how the general idea came to be.  Other than that, it's pretty standard fare, pretty formulaic.  There is the slight nod to the Foo Fighters, and I'm sure 99% of the rest of it is a nod to someone I don't know, but that's how it goes these days you know.  It's tough out there.