I finally managed to make the script work, but for some reason it won't work in "Play", I've tried with the PlayerAdded function, but it dosen't work either way.
Here is the script I used, which managed to work. (In "Run")
sizeIntroP1 = 0 while ( sizeIntroP1 < 300 ) do game.StarterGui.intro.introP1.Size = UDim2.new(1, 0, 0, sizeIntroP1) sizeIntroP1 = sizeIntroP1 + 1 wait(0.01) end
UPDATED
p = game.Players.LocalPlayer sizeIntroP1 = 0 p:WaitForChild("PlayerGui") p.PlayerGui:WaitForChild("intro") p.PlayerGui.intro:WaitForChild("introP1") while ( sizeIntroP1 < 300 ) do p.PlayerGui.intro.introP1.Size = UDim2.new(1, 0, 0, sizeIntroP1) sizeIntroP1 = sizeIntroP1 + 1 wait(0.01) end