attempt to index upvalue 'part2' (a nil value) Why does this keep doing this? I'm so confused

Hey there, it appears that you're trying to access an instance later on in the script as a directory. This is not possible as 'Part2' is not an actual directory. You could do the following to fix this

--Simply add this to your script where it appropriately belongs and edit if needed--

 A = larm:GetChildren()
for i,v in pairs(A) do --Gets larm's children
    if v.Name == "part2" then --Checks if a child has this name
         v:Remove() --Removes the child
    end
end

If this worked make sure to accept! If it didn't please comment and I'll try my hardest to help you fix it further. Hoped this helped!!

-- Tremor Punch, made by Coldcce.

player = script.Parent.Parent
mouse = player:GetMouse()
animation = script:WaitForChild("Animation")
animation2 = script:WaitForChild("Animation2")
isplaying = false

bin = script.Parent
Backpack = bin.Parent
me = Backpack.Parent

damage = 15
buttonOn = false

char = player.Character

larm = char:FindFirstChild("Left Arm")
rarm = char:FindFirstChild("Right Arm")

enabled = true

local uis = game:GetService("UserInputService") --The service
local plyr = game:GetService("Players").LocalPlayer

local part2 = part2--Remove this as it is unnecessary.

uis.InputBegan:connect(function(Key, Processed)
    if Key.KeyCode == Enum.KeyCode.X and not Processed then
        if buttonOn == false then
        buttonOn = true         
        if isplaying == false then
            isplaying = true
            local animationp = player.Character.Humanoid:LoadAnimation(animation)
            animationp:Play()
            player.Character.Humanoid.WalkSpeed = 0
            wait(1)

            local part2 = Instance.new("Part")--As u can see u already defined it correctly later on in the script to create a part.
            part2.BrickColor = BrickColor.new("Light blue")
            part2.Parent = larm
            part2.Name = "part2"
            part2.Size = Vector3.new(2.5, 2.5, 2.5)
            part2.TopSurface = "Smooth"
            part2.BottomSurface = "Smooth"
            part2.FormFactor = "Symmetric"
            part2.Shape = "Ball"
            part2.Transparency = 0.8
            part2.CFrame = larm.CFrame
            part2.Material = "Neon"     

            local f = Instance.new('BodyForce')
            f.force = Vector3.new(0, 0, 50)
            f.Parent = part2

            local Owner = Instance.new("ObjectValue")
            Owner.Parent = part2
            Owner.Name = "Owner"
            Owner.Value = me

            local sound = Instance.new("Sound")
            sound.SoundId = "http://www.roblox.com/asset/?id=315030459"
            sound.Parent = part2
            sound.Volume=1
            sound.Pitch=1
            sound:Play()

            local e = script.ArrowScript:clone()
            e.Parent = part2
            e.Disabled = false

            local weld = Instance.new("Weld", char)
            weld.Part0 = weld.Parent["Left Arm"]
            weld.Part1 = part2
            weld.C1 = CFrame.fromEulerAnglesXYZ (0, 0, 0) *CFrame.new (0, 1.5, 0)
            weld = Instance.new("Weld", char)
            weld.Part0 = part2
            weld.C1 = CFrame.fromEulerAnglesXYZ (0, 0, 0) *CFrame.new (0, 0, 0)
    for i = 1,6 do
        wait(0.2)       
        part2.Transparency = part2.Transparency - 0.1
        player.Character.Humanoid.WalkSpeed = 18
        end
        end
        end 
    uis.InputEnded:connect(function(Key, Processed)
    if Key.KeyCode == Enum.KeyCode.X and not Processed then

            local animationd = player.Character.Humanoid:LoadAnimation(animation2)
            animationd:Play()
            player.Character.Humanoid.WalkSpeed = 0
            player.Character.Torso.Anchored = true

            wait(3)
            part2:remove()
            player.Character.Torso.Anchored = false
            player.Character.Humanoid.WalkSpeed = 16
            wait(5)
            buttonOn = false
            isplaying = false
    end
    end)
end
end)

If this helped be sure to accept it. If it didn't post a comment about it and I'll try to help you out as best as I can ty!