specter oil won't help against simple undead ... so i'd bite the bullet and just re-oil the wticher's sword with necrophage oil.Ozzrel can be stunned if your aard is sufficiently pumped (given the earliness of the plot) ... i've used igni, but i can't recall it doing anything particularly good or bad, but do use your witcher's sword (or better still, use a meteorite sword if you've collected 3 pieces of ore)early in the game i prefer the Aard / coup de grace combo with ghouls