How to script this Gui?

First start with the changed event. Then we use the death event. This is simple. Just make a frame that covers up the whole screen and make it red. Then we need to do these scripts.

Changed Event

This event fires when the object's property changes. We can take the thing that changed and we can see what changed and what the change was.

--ROBLOX Wiki
Workspace.Changed:connect(function(property)
  local value = Workspace[property]
  print("Workspace's " .. property .. " changed to " .. tostring(value))
end)

Workspace.Name = "Workspace2"
--> Workspace's Name changed to Workspace2

OUTPUT:

Workspace's Name changed to Workspace2

Death event

This checks if a humanoid dies.

workspace.Player.Humanoid.Died:connect(function()
    print("Someone died!")
end)

Hope this helps!