How would I make my projectile explode in the air?

Ok so far,I've made a script that shoots transparent parts with a selectionbox. Now all I want it to do is make sure it flings the character in a 360 spin while shooting it at the player. As well as I also want it to grow from a small part to a big part sorta like going in a wait() loop. Can any one of you please explain how?

mouse = game.Players.LocalPlayer:GetMouse()
function KeyDown(key)
if key:lower() == "g" then
x = Instance.new("Part")
x.Size=Vector3.new(20,20,20)
x.BrickColor=BrickColor.new("New Yeller")
x.TopSurface="Smooth"
x.Transparency=1
x.BottomSurface="Smooth"
x.CFrame=game.Players.LocalPlayer.Character.Torso.CFrame*CFrame.new(0,0,0)
x.Parent = game.Workspace
y = Instance.new("BodyVelocity")
y.Parent = x
y.maxForce=Vector3.new(math.huge,math.huge,math.huge)
y.velocity=game.Players.LocalPlayer.Character.Torso.CFrame.lookVector*80
z = Instance.new("SelectionBox")
z.Parent = x
z.Adornee = x
game:GetService("Debris"):AddItem(x,2)
end;
end;
mouse.KeyDown:connect(KeyDown)