After getting some experience with him, I think SmogMan could use a change or two. So...appearance/personality changes!
Appearance: SmogMan appears fairly large, around 7 feet from top to bottom. But as for what he is...
He appears to be a stylized smog cloud, grayish-purple in color. Due to his nature, he can alter his form to appear as almost anything in any color, but by default, he appears as a monstrous human-like head, with imposing, glowing eyes, and a mouth covered in fangs. Short, stringy arms come out from the lower sides, ending in large hands with pointy fingers. On the backs of his hands are his emblem: a purple, nebulous cloud.
SmogMan used to have a small, black sphere that served as his core, but after receiving an update, it dissipated into the rest of his form. This has enhanced his ability to alter his shape, at the expense of now being able to take damage anywhere his gas occupies.
Personality: After obtaining his upgrades, SmogMan became a more poisonous personality, fitting given his composition. He now tends to act like a colossal jerk towards anyone he doesn't know well. Surprisingly, his fondness for Alda and Rhonda remains intact, however, so he still acts nice to them. His attitude also tends to improve as he spends more time around someone...it's just a matter of getting someone to hang around that long given his physical and emotional toxicity.