Vullaby learns defog by level up, so I don't know why you need it as an egg move unless you are little cup-ing or something. Also, why impish ferroseed when he benefits from lower speed, so isn't relaxed, 31/31/31/xx/31/0 better?
I do have perfect impish vullaby with knock off, foul play and relaxed ferroseed with leech seed and stealth rock with the spread mentioned above.
Lol then I want both of those :)