How would you add a trail to a projectile?

For the past month or so I've started working on my own game, I script a lot of projectile moves, like if you've watched naruto. But anyway how would you add a trail to this kind of script, I know how to use custom particles, but that's not enough

local enabled = true
Player = script.Parent.Parent
me = Player
mouse = Player:GetMouse()
Run = game:GetService("RunService")
waittime = 10

function Talk(msg)
game:GetService("Chat"):Chat(Player.Character.Head, msg, Enum.ChatColor.Blue)
end

function onKeyDown(key)
if not enabled then return end
enabled = false
	Key = key:lower()
	

	
	if key == "q" then
		Talk("Lend me your power Isobu.")
		wait(1)
		Talk("Water Style:")
		wait(1)
		Talk("True Water Dragon Jutsu!")
		Run = game:GetService("RunService")	
		RightShoulder = me.Character.Torso["Right Shoulder"]
		LeftShoulder = me.Character.Torso["Left Shoulder"]
		RightShoulder.C0 = RightShoulder.C0 *CFrame.Angles(0, 0, -55)
		LeftShoulder.C0 = LeftShoulder.C0 *CFrame.Angles(0, 0, 55)
		Run.Stepped:wait(0)
		for i = 1, 1 do
		local x = Instance.new("Part")
		x.BrickColor = BrickColor.new("Navy blue")
		x.Size = Vector3.new(30,30,30)
		m = Instance.new("FileMesh")
		m.Parent = x
		m.MeshId = "http://www.roblox.com/asset/?id=24478215"
		m.Scale = Vector3.new(55,55,55)
		x.TopSurface = "Smooth"
		x.BottomSurface = "Smooth"
		x.Name = me.Name
		x.CanCollide = false
		x.Transparency = 0
		fd = script.Firedamage:Clone()
		fd.Parent = x
		y = Instance.new("BodyVelocity")
		y.maxForce = Vector3.new(math.huge, math.huge, math.huge)
		y.velocity = me.Character.Torso.CFrame.lookVector* 80
		x.Parent = game.Workspace
		y.Parent = x
		x.CFrame = me.Character.Torso.CFrame*CFrame.new(0, 14, -6) * CFrame.Angles(0,0,i * 0)
		fd.Disabled = false
		game.Debris:AddItem(x, 4)
		wait(1)
		end
		 for i = 1, 1 do
			RightShoulder.C0 = RightShoulder.C0 *CFrame.Angles(0,0,55)
			LeftShoulder.C0 = LeftShoulder.C0 *CFrame.Angles(0, 0, -55)
			Talk("Nice Job,")
			wait(1)
			Talk("Isobu.")
			Run.Stepped:wait(0.01)
		end
		wait(2)
   wait(10)
end
enabled = true
end
mouse.KeyDown:connect(onKeyDown)

for me.