Piggy packing off of the myth angle, why not try and smash a lot of creatures together? Medusa had snakes for hair, Centurs are a combo of people and horses, and Chimera's are just a mix of crazy things. I can see that your Overlords have a real metal and flame vibe, as well as being draconic/dino shaped (with possibily a little goat in there for good measure?) You could keep those elements to make it your own.
I'd also recommend looking at myths from locations that are similar to where your creatures would inhabit. Eg, looking at polynesian legend for creatures who inhabit volcanoes.
Random Idea
What about an aquatic Overload, like a mermaid, but half fish (maybe octopus or shark), half skeleton with electric eels for hair?