Dying Light Italian Plumber Trophy / Achievement will give you one Bronze trophy or 10 gamerscore points. To get this Trophy / Achievement you must kill kill an enemy with a wrench, using Vault followed by Drop Attack.
To get the Italian Plumber you will need to posses two skills “Vault” (Agility Level 4) and “Drop Attack” (Power Level 10). When you have these, get hold of a wrench and charge towards the enemy, vault over them (R1 on PS4 / RB on Xbox One) and use a weapon attack while in the air (R2 on PS4 / RT on Xbox One).
From the Drop attack, your enemy will be killed instantly. Wrenches are very easily accessible from the beginning of this game and their damage stats does not matter.
To find the wrenches look inside the locked chests. Save some for these achievement and if you cant find one, ask for help from your friends.
If you are still not sure, watch the following video on how to get the Dying Light Italian Plumber Trophy / Achievement. This game is now available on PC, PS4 and Xbox One.