Answer:
Metal or bone I may be, many teeth I have and always bared. Yet my bite harms no one. And ladies delight in my touch.
When the creeper passes, all the grass kneels
Different lights do make me strange, thus into different sizes I will change
I run around the city, but I never move.
Long and slinky like a trout, never sings till it's guts come out.
I am your mother's brother's only brother in law. Who am I?