Season 6 finale: just a few spoiler thoughts · 2:55am Oct 23rd, 2016
I suppose I should start out with the disclaimer that I kind of skipped watching a minute here and a minute there through the first half of the arc and watched the second without skipping.
I'm going to do a break so no one who doesn't want to see spoilers can avoid them.
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Thorax's ascension. I'm not entirely sure of the fallout with the fans but I like it! It leads to some many questions and possibilities for the changelings. Their history, their future, and biology (which are related in my mind).
Historically, what if the "black" stage was an intermediate stage of growth before metamorphosing into the final form? That the shapeshifting aspect was a survival mechanism until they grew enough to give rather than take? What if one ruler wanted complete power so she/he decided to "stunt" the growth of their offspring while systematically eliminating the fully developed changelings?
Future? Oh ho ho. There is no reason not to have tons of fun with it. What can they do in the new form? Is the ability to shapeshift retained or lost?
Biology. What if the changelings are something like the axolotl? The dark form could be the mature "juvenile" with the new form being the true and final stage.
And I actually like the design. Very beetle-like. Like one of those jewel beetles. I imagine the new and improved changelings to be iridescent. I mean, take a look at these! So pretty!
There is no reason not to have fun with it! 
Funny thing is, I touched upon some of the themes of this episode in Stinkbug the Unwanted. It was weird.
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Dun dun DUN! Hopefully a good kind of weird.
I suspect that the writers wanted to flesh out the changelings as much as the fans. One off villains are usually boring.