Some time ago, I saw someone mention making a monstrum when asked about creating monster races. Supposedly it is a PC that is the child of a human and a monster, or something like that. I was wondering where I can find the rules for doing so. For example, a Half Yuuki-Onna. It's like a half-elf, but instead of an elf, the non-human parent was a monster. The idea is that some of the monster's abilities would be passed down to the offspring but not all and in a weaker variation.
This is not a duplicate of this question about making new playable races, because that post is asking about making new races in general, not specifically tailored to monster-human offspring like mine is. If this is a duplicate then please explain to me where the overlap is located because for the life of me I can't see it. In the linked post I see creating a monster race and advance race guidelines (linked twice) neither of which answer my question.