So, I finally settled on a design for Changeling!Nelson Tethers. The actual drawing bugs me a bit, but this gets the major points down.
I wanted his appearance to stay as human as possible, with his tail as the only major detail that could stand out. All of his nonhuman features are meant to be SUBTLE. So subtle that unless they were pointed out, or you were looking for them, you would never notice them. Because one of the traits that mark a Changeling is their ability to pass as a normal human.
Nelson doesn't have a lot of powers, but one I wanted to give him was the ability to make his tail "vanish" so he could further pass as an ordinary human. The only flaw with it is that his still visible in his shadow. But he keeps it close to his body to prevent people from noticing.