Pony monster idea I came up with just now:
Primordial Land Golems
These mechs are found in mountains that have taken over them for billions of years since earth’s beginning.
They’re silent, they can’t talk except make low pitched roars of the gears that click and turn in their overgrowthed system.
They don’t look like ponies, they have the legs of ponies but they body and head shape of a horse. They have a very unexpectable system of moods that show as redeeming as allies or as threats.
Their heavy mass is what’s said to create the lands that surround us, somehow shut down for billions of centuries.