I mean, i hear ya on your list overall, but the Aliens & Predator one...
You seen how those Aliens reproduce? Face *Huggers* is just them giving it a SFW name!
Dear Friend.
I hope that upon receiving this letter you feel well in body and soul.
Certainly, in the complex reproductive process of aliens, there is a parasitic phase in which the larvae are introduced into a host which they devour until they acquire a stage of development sufficient to live outside. However, you will remember the existence of a queen that lays eggs and this is where, just as in the case of ants, bees and wasps, we must assume the existence of drones. Yes, male aliens impregnating the queen, probably only once in her life.
Leaving aside the possibility of establishing relationships between males, the problem would be to know if the aliens have an anus or secrete through their mouths, regurgitating fecal matter through the extensible appendage they house there.
This is where I find the representation of felatios between Predators and Aliens absolutely necessary and that is why I have decided to demand its introduction in the VN. Will predatory penises become impregnated with poop? Obviously, it is a topic of undoubted scientific interest.
Anyway, I hope to have shed some light on this fundamental cosmic mystery and, without further ado, I send you my warmest regards.