So I'm trying making an on monster kill put on inventory script?

local Humanoid = script.Parent.Human
function PwntX_X() 
    local tag = Humanoid:findFirstChild("creator") 
    if tag ~= nil then 
        if tag.Value ~= nil then 
            local theinventory = tag.Value:findFirstChild("PlayerGui").Inventory2
            local theinventoryparts = theinventory:GetChildren() 
            for i, v in pairs(theinventoryparts) do 
                wait(0.5) 
                if v.SlotValue.Value == "" then 
                    v.SlotValue.Value = "Wood" --Change this to desired variable so you can have any weapon 
                    v.Ammt.Value = 5 
                    v.SlotLabel.Text = v.Ammt.Value 
                    v.SlotImage.Image = "http://www.roblox.com/asset/?id=539465370" 
                    break 
                elseif 
                    v.SlotValue.Value == "Wood" then 
                        v.Ammt.Value = v.Ammt.Value + 5
                        v.SlotLabel.Text = v.Ammt.Value 
                        break --This script we just wrote will make it so you can stack wood 
                    end 
                end 
            wait(0.1) 
            script:remove() 
        end 
    end 
end 

Humanoid.Died:connect(PwntX_X)

You should also give the output so that it is easier to help you.

One thing I speculate is that it doesn't work because there is no child in the character (or it may not actually be a character) named "Human".

Also, I think maybe it does not work because the tag doesn't exist when you kill the monster.