And I don't mean things like a incubus things.

Humanoid incubus design*

Umi no Soko is pretty monstrous plus the art is insanely good https://www.mangago.me/read-manga/umi_no_soko/
You can also try the monster sex tag on mangaupdates: https://www.mangaupdates.com/series.html?category=monster+sex&genre=Yaoi&exclude_genre=Doujinshi&perpage=50

https://www.mangago.me/read-manga/kemono_jingai_bl/
https://www.mangago.me/read-manga/pendulum_kemonohito_omegaverse/
https://www.mangago.me/read-manga/boku_no_danna_sama/
I know I've read at least 5 different BL like this, but ya know when you're looking for something you just can't find it XD

Thanks! <3

Thank you! <3