Fire, fire, fire, fire, fire.
Against anything zombie-like, use fire. It's damn-near mandatory, although I realize that it's hard as all hell in the Cyseal region where it rains (although the rain isn't nearly as "powerful" as the rain spell - remember this; just because it rains doesn't mean that you cannot benefit from casting Rain, as odd as it sounds).
Setting them on fire prevents them from healing from their own poisonous ooze. Do note that you want to set fire to them before you engage them in melee, otherwise you'll probably have ooze everywhere, then set them on fire, and then your people are on fire, and everyone is having a bad time.
