I remember that there was a feat called "Drinker of Souls" in the earlier rules and I cann't seem to find it anymore. Where was it from originally? I cann't find it on-line. Does anyone know where to look?
I only see a trait called "soul drinker" and nothing specifically named what you are looking for. If I knew what the feat your are looking for generally did I might be able to look around through other soul related feats etc.
I immediately thought about the Tiefling race trait that gives you temporary HP for killing blows via Coup de Grace.
Which is cool in its own right, but I don't know if it's what you are looking for.
What did the feat you are looking for do originally?