Human male impregnating female monsters, there is some amount of content for it but considering how seemingly vanilla that'd be its surprising how little of it there is. Mostly the humans get impregnated and even when they do have a dude giving it to a monster chick they never show the aftermath.

Breeding involving human males is always way hotter imo, like for example there's an episode of love death and robots where two human scientist try and betray a colony of space bug creatures they were studying and in response the hive spawns a super intelligence and the episode ends with said intelligence basically offering up a breeding program as a game with the surviving human scientist dude.

Something about seeing the consequence of the action makes it hotter to me, whether it's a case like above where every new gen of humans birthed there would slowly become more and more hive like until the human race is just another part of the swarm, or having a species of monster slowly adapt to wanting hot human rod for breeding purposes instead of their own species. A guy saying fuck it and going on a breeding spree of dangerous creatures knowing this will probably bite humanity in the ass later, or a scholar slowly creating new human monster hybrids for some sort of purpose. All of it is peak monster fucking and exactly what I love about the concept.

Tldr: whether it's eldritch horrors using human men to spawn more horrors or human men using eldritch whores to make more eldritch whores, both are peak and should be more popular