On the Discord (https://itch.io/t/284398/discord) it has been discussed many times and the results have been posted several times. It gets quite a bit crazier by using large amounts of mana to mutate the slave.
It depends on what you want to use the slave for and personal preference. For me the perfect slave is a beastkin fox that has mastered magic and melee combat. For you that's probably not it.
quick, robust, devoted, dominant, pretty voice, 81 of beauty (before upgrade) fully upgrade still track responsive and strong trait but failed until then
that other than the stuf who go with is the best you can get
