When Player Hovers Mouse over another Character, a GUI Appears?

Basically, There is a Billboard Gui on player's head, but ive set it To invisible, so only when players hover their mouse, it should appear, but i get this error: Character is not a valid member of Model

local Mouse = game.Players.LocalPlayer:GetMouse()

while wait() do
	if Mouse.Target and Mouse.Target.Parent:IsA("Model") and game.Players:GetPlayerFromCharacter(Mouse.Target.Parent) then
		print("hi")
		Mouse.Target.Parent.Character.Head.BillboardGui.Enabled = true
	end
end

You tried to get the Character inside the Character in line 6. You already have the Character when writing" Mouse.Target.Parent", so remove Character in line 6.

local Mouse = game.Players.LocalPlayer:GetMouse()

while wait() do
    if Mouse.Target and Mouse.Target.Parent:IsA("Model") and game.Players:GetPlayerFromCharacter(Mouse.Target) then
	local Player = game.Players:GetPlayerFromCharacter(Mouse.Target)
        print("hi")
        Player.Character.Head.BillboardGui.Enabled = true
    end
end

Maybe this will work. I defined a variable called "Player" and changed Mouse.Target.Parent to Mouse.Target because the target is the entire model.