It's unclear from your description just how the spitting works; while you say "doomed to die" it's unclear what you mean when you go on to say that creatures with more than 6 HD can make a will save each day... Do you mean that it's a curse such that *if* that character dies he rises as a zombie, until either the save's made or the curse removed or it takes effect? Or does it instantly slay anything with 6 HD or less?