So i redesigned him, and Pharynx, a little bit. Took some of their original colours and tried to make them more appealing. Took off the horns (I HATE THEM, why horns?! I get it, they are meant to be like beetle mandibles, but i just think they look dumb), and gave them some kind of ornament, like a crown, to represent their status.And added fangs, because why not. Thorax has some round and spiky parts, as the ruler of the hive, this means he can protect the hive if he needs to, but that he is also a compassive and mostly peaceful king. Pharynx, being a soldier, has a more spiked body, with a sting at the end of his tail. The common changeling is pretty round, not that much spikes.
Thorax had a mutation that made him able to rule, since he should have been a soldier changeling like his brother. Both of them are really young (i headcanon this because when Thorax disguised himself as Crystal hoof, he wasn’t a fully grown pony, more like a teen), they are !7.