what kinda hybrids? birddog? lizardcat?
you could also lean a bit into mythology. you're telling me these obviously insane people created a bunch of bio-mechanical monsters and never once went "well shit, how about a monster from myth?" because i call cap if so.
i mean, you could really go full ham with it, too. greek myth alone has thousands of monsters, beyond the mere ten or twenty the everyman could list off. egypt was fucked but in a whole different way, and let's not even start on japan and china.
you're not dedicated to it being purely mechanical - fucking dinosaurs, enough said - so that already opens up the possibilities.
if you want a small list of monsters i can see scientists of today trying to do, let alone these obvious madmen, i can give you a few. heck, quite a few of them would fulfil various kinks, too.
Cerberus: Greek. Knotting.
Lamia: Greek. Futa, double-penetration if you go for hemipenis.
Sphynx: Egyptian. Futa (Maybe?), feline penis so...barbs?
Griffin: Egyptian (I know, shocked me too). Flying sex, barbs.
Yuki-Onna: Japan. Futa, ice so...ice crystal effect? make you hungrier after sex?
Kitsune: Japan. knotting, maybe something with illusions?
Oni: Japan. Size-difference (as in, this boi's massive so his dick is gonna be giant), maybe cum inflation.
Following on from the dinosaurs you added, you could also add dragons? the typical western dragon with the four arms and the wings, or the eastern which is basically a giant snake with two arms and a majestic moustache.
and if all else fails? slime.