They said you need the Blade of Xeres to kill Vincent to prevent the demon from escaping well I killed Vincent with the Blade of Xeres and he died. Then I tried with the aerial decapitator the demon came out but since it was weak I killed it. So what's the point to kill Vincent with the blade you still get the money if you don't use it.
Every time I've killed him accidently with my jolt or the wrong weapon the demon appears (weak as you said) but he laughs, call me a fool or something and disappears, supposedly to wreak havoc on the world. When you killed him was he dead on the floor or did he disappear?
He says something like You fool I am free after that his freedom ends when he realizes that my Aerial Decapitator killed him. It says on his dead body L'anamech(forgot spelling) Dead then his body disappears.
I'll have to have a try. I wonder if you get the same exp by doing it that way. But it shouldn't be possible at all.... (lost in thought)
L'anamelach I believe. And it's possible to kill him if you use throwing weapons. Just launch as many as possible and after one kills vincent then when they return they have a chance of hitting him and killing him before he disappears. It's a bug rather than another way of officially doing the quest.