Arelith

That's pretty much the peak of the class though, build gets worse at higher levels as saves and AC go up and that lifesteal becomes less frequent.

Though I don't know why you're able to lifesteal off undead.

There is a lot that could be argued of the negative energy imbue.
I think it should not work against anything that doesn't take neg energy damage at least.

I've always wondered why negative warlock blasts, essences, and now weapon imbues work against undead. Is it some kinda special anti-negative negative or what?