Succubus is 50% demon, 40% bunny. I don't know all the combinations, but it seems that most are at least 50% one thing and at least 20% or 40% of another. The combinations are coded in expansionsetup.gd.
~2/3 recipes for subspecies are given through slave guild quests. The remaining recipes are either easy to guess, likely to be stumbled on by accident, or hinted at in Race Descriptions (accessed by clicking on Elf or Dragonkin or similar in the character description).
