I believe the VA did an interview a few weeks back mentioning that she was hired to do a tougher, grimmer voice (that's presumably fit with the old 'Cool Karlach' face) but that it was difficult on her vocal cords and between that and her natural energy, it resulted in big changes to Karlach's character. The infernal engine was also a very late development, so late that she didn't know what it was or looked like.
Thanks for the info! Interesting stuff.
