My death screen script appears in the studio but not in the game?

When you join a game it will take a small amout of time until the character is created. This delay is not included in studio. We commonly use the following code to wait for the character:-

local localPlr = game:GetService('Players').LocalPlayer
local char = localPlr.Character or localPlr.CharacterAdded:Wait() -- if the character is nil ie not loaded wait intil the character is added and return the character model to the char variable

Putting it all together

local localPlr = game:GetService('Players').LocalPlayer
local char = localPlr.Character or localPlr.CharacterAdded:Wait()

char:WaitForChild('Humanoid').Died:Connect(function()
    script.Parent.Parent.Frame.Visible = true
end)

Note this should be a local script in the gui.

I hope this helps.

Use the transparency property instead of the visible property.

im sure this will work if not then ill fix it

script.Parent.Parent.Frame:WaitForChild()
game.Players.LocalPlayer.Character:WaitForChild('Humanoid').Died:connect(function()
    script.Parent.Parent.Frame.Visible = true
end)