UnderchatFrame no idea what its for...

local Players = game:GetService("Players")
local me = Players.LocalPlayer

function CreateChatBox(Player)
    repeat wait() until Player.PlayerGui
    repeat wait() until Player.Character

    local UnderChat = Instance.new("ScreenGui", Player.PlayerGui)
    UnderChat.Name = "UnderChat"
    local Character = Player:FindFirstChild("Character")
    local Head = Character:FindFirstChild("Head")

    local UnderChatFrame = Instance.new("Frame", UnderChat)
    UnderChatFrame.Size = UDim2.new(0, 902,0, 138)
    UnderChatFrame.BorderColor3 = Color3.new(255,255,255)
    UnderChatFrame.BackgroundColor3 = Color3.new(0,0,0)
    UnderChatFrame.BorderSizePixel = 5
    UnderChatFrame.Position = UDim2.new(0.394, 0,0.771, 0)
    UnderChatFrame.Visible = true

    local ViewportFrame = Instance.new("ViewportFrame", UnderChatFrame)
    ViewportFrame.Size = UDim2.new(0, 135,0, 138)

    local ViewportCamera = Instance.new("Camera", ViewportFrame)
    ViewportFrame.CurrentCamera = ViewportCamera

    local offset = Vector3.new(0, 0, -3)
    ViewportCamera.CFrame = CFrame.new(Head.CFrame * offset, Head.Position)

end
CreateChatBox(me)