Answer:
I am the ultimate killing machine used not once but TWICE I can be made by humans.
In wealth I abound; in water I stand; as a fencer I'm valued all over the land; at Venice I'm famous; by farmers I'm prized; respected by law yet huntsmen despised; consternation and ruin ensue when I break; And the beasts of the forest advantage won't take.
I am a mini solar powered computer
What is always in front of you but can't be seen?
I am a candy that looks like a shepherdβs staff.
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.