A couple of ideas: Are we sure that Kaseryn is not an Insequent? His specialization is consistent the single-minded focus of that race. And his appearance (though not his name) is consistent. However he does use a Croyel. More importantly, what if the introduction of the Insequent hasn't happened in...

I think there is merit to this line of thinking. My recollection of the closing of the Arch of Time on Foul story is that he pursued/plagued some of the Creator's children and was trapped when it was sealed. There seems to be familiarity between Foul and the Insequent. It's possible that SRD is draw...