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.