Adding decals to players when they do something?

I am making a horror game with endings and in one of the endings you killer the monster. I have the script where you kill the monster the ending triggers, but what i want is when you kill it you get a blood decal on your arms. My problem is i dont know how to do that.

game.Players.PlayerAdded:Connect(function(plr) script.Parent.Died:Connect(function(hit) hit.Parent.RightArm <----- here

plr.PlayerGui.Black.Frame.Active = true
game.Workspace.Background_music:Stop()
game.Workspace.chase.Sound:Stop()
plr.PlayerGui.Black.Frame.BackgroundTransparency = 1
wait(.1)
plr.PlayerGui.Black.Frame.BackgroundTransparency = 1
wait(.1)
plr.PlayerGui.Black.Frame.BackgroundTransparency = 1
wait(.1)
plr.PlayerGui.Black.Frame.BackgroundTransparency = 1
wait(.1)
plr.PlayerGui.Black.Frame.BackgroundTransparency = 1
wait(.1)
game.Workspace.Revenge:Play()
plr.PlayerGui.Black.Frame.BackgroundTransparency = 1
wait(.1)
plr.PlayerGui.Black.Frame.BackgroundTransparency = 1
wait(.1)
plr.PlayerGui.Black.Frame.BackgroundTransparency = 1
wait(.1)
plr.PlayerGui.Black.Frame.BackgroundTransparency = 1
wait(.1)
plr.PlayerGui.Black.Frame.BackgroundTransparency = 1
wait(2)
plr.PlayerGui.Black.Frame.TextLabel.TextTransparency = .9
wait(.1)
plr.PlayerGui.Black.Frame.TextLabel.TextTransparency = .8
wait(.1)
plr.PlayerGui.Black.Frame.TextLabel.TextTransparency = .7
wait(.1)
plr.PlayerGui.Black.Frame.TextLabel.TextTransparency = .6
wait(.1)
plr.PlayerGui.Black.Frame.TextLabel.TextTransparency = .5
wait(.1)
plr.PlayerGui.Black.Frame.TextLabel.TextTransparency = .4
wait(.1)
plr.PlayerGui.Black.Frame.TextLabel.TextTransparency = .3
wait(.1)
plr.PlayerGui.Black.Frame.TextLabel.TextTransparency = .2
wait(.1)
plr.PlayerGui.Black.Frame.TextLabel.TextTransparency = .1
wait(.1)
plr.PlayerGui.Black.Frame.TextLabel.TextTransparency = 0
wait(5)
game.Workspace.Ending2Kick.Position = Vector3.new(376.5, 33.75, -84)

end) end)