This is a:
NEEDLE (of the type used for sewing)
This is the everyday spear, beware!
It hurts and draws blood if not handled with care.
A sewing needle is long, pointed and can be sharp (like a spear). You might accidentally prick your finger and draw blood if you aren't careful.
It dips below flowing planes, jumps back up before long,
This describes a typical sewing motion, moving the needle up and down through a sheet of material (a 'flowing plane').
Repairs old and creates new, if one knows how it's done.
You use a sewing needle to repair old garments, and with a little expertise you can even create whole new items to wear!
It's shiny and smooth, but unbending and hard,
in it's tail there's a hole as an integral part.
Typically a sewing needle is made of metal - shiny, smooth, unbending and hard - and at the opposite end to the point there's a hole (the eye) to put the thread through...