Now I remember. I played on 2.1b and lost all my spell booka and espers in chapter 9 and 10. Yeah, impale is for sure pretty useful. If maegca ignores magic resistance / armor then it is also another useful item. 2 maegca deal 2 percent of hp every 30s, even stronger than impale. Unfortunately that is not how it works currently.
I cannot do much damage to Zyl, not enough for his imba regen. I dont know if it is a bug in 2.1b or not, didnt try it in 2.1c. Can you tell us your items set up for this fight?