Attemp to index nill with "TweenSize"??

local player = game.Players.LocalPlayer or game.Players.PlayerAdded:Wait()
local char = player.Character or player.CharacterAdded:Wait()
local Energy = player:WaitForChild("Values").Energy
local EGgui = script.Parent

Energy:GetPropertyChangedSignal("Value"):Connect(function()
    local EGChange = Energy.Value/100
    EGgui:TweenSize(UDim2.new(EGChange,0,1,0),"In","Linear",1)
end)