It's all backstory, I could easily see a creation like a Clockwork monster turning on it's creator, killing, and bits of flesh and bone still grinding through some of the gears. This causes one of the Evil gods to (Lamashtu maybe? Is there a god that would like clockworks?) notice it and decide to make it a lesser servant, granting it some small power(s).
Well, before you start focussing on the mythic rules alone, think of what you want this monster to be. Is it a unique creature, hard to find and surrounded by legends? Then take a look at earth's original mythical creatures who will certainly inspire you with an ability or a theme or two.
Or is this mythic monster something you can encounter on a regular base, depending on where you look? What is it's purpose then, in terms of the stories you intend to tell, the battles you envision to fight, and the look & feel of the setting where all this shall take place?