Hi, Envy. I see that your poem is one of those based on a very clever rearrangement of whole lines, to create new meanings from previously-stated thoughts, and ingeniously ending up where it started from. (You can tell that I have never had the courage to try to write one myself.)
I was intrigued by your title, The Lament Of The Darkest Servant. I even checked the dictionary to see if there perhaps was another definition of the word “lament” other than the well-known one of “sorrowful statement”, but there was not, so I went back to the poem looking for indications that Bellatrix felt any sadness or dissatisfaction with her role in the Dark Lord’s service.
Perhaps line two of verse three holds a clue. To paraphrase it: Her rage and her knowing bathe all who seek what she fears. This is the only clue that there is something she fears, something about which she is not totally happy. (Line four says that she takes His poison, which might sound unappealing, but apparently she does so gladly, so that can’t be the thing she is lamenting about.)
Most of this poem practically explodes with her negative energy, even madness, showing the great power for evil that she embodied. Your language is certainly vivid, so much so that the reader scarcely notices that the lines are being repeated. Although the point of view seems to be that of the poor unfortunate people who behold her, we get such a look into her heart that we can scarcely stand to see any more.
Creepy, evil...very Bellatrix. The repetition makes it seem like a kind of a mantra.