There's currently a glitch involving the vampirism stone and weapons with effects that activate on kill (like the golden shiv or the assassin's dagger), where killing an enemy with the vampirism effect will cause the effects to proc twice. I'm not sure if this effect is balanced or not, but just thought I'd highlight it here as I can't find much mention of it elsewhere.
Love the game so far and am eagerly waiting for more! :)