Answer:
In a tunnel of darkness lies a beast or iron. It can only attack when pulled back. What is it?
I am longer than a decade and shorter than a millennium
My first is second in line; I send shivers up your spine; not quite shining bright I glitter in the light.
I am rubber you can eat!
What can fill a room but takes up no space?
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.