In a game with Late Caelum (Raptor), I had a diseased Harab Elder. So I made him cast "Twiceborn", and when he got real sick (mute, limp...), I found an easy way to kill him : Cloud Trapeze in an enemy *underwater* province with friendly dominion !
Everything went as planned, he drowned instantly upon arrival without even triggering a combat, the province still in my dom (it was 5+), but ... I didn't get any Wight mage, my mage is utterly lost !!!
The bug is perhaps tied to the "unusual" way he died, for the next one I'd try to have it killed in combat...
BTW a question : what becomes a "Twiceborn" Oracle pretender ? As an "undead fountain" doesn't exist I suppose I get a standard "human" wight ?
Or maybe nothing at all, as with my poor Raptor ?