I need to set aside a couple of hours to have a thorough read of Julian Gollop's ongoing design plans for his Chaos remake - he's sharing a remarkable amount on his Gollop Games blog. Today though, I take the easy route - monkey see previously unrevealed concept art for the original X-COM/UFO, monkey must post about it. Because said concept art features, as well as some very different looks for X-COM's familiar rogues gallery (e.g. what I think might be an Ethereal design has big thighs) there are some never-before-seen additions. Including what appears to be a giant mutant rabbity thing.
Julian Gollop doesn't provide too much detail on the what, why, whatever happened for these creatures, although apparently there was GDC talk in which more was explained. Oh good, now I have reason #456546541351512513 to be depressed about not going to GDC. In comments he does provide an explanation for the less monstrous type of bunny on show, however:
"John [I am guessing Reitze, one of X-COM's artists] made some animations of bunnies being squashed with showers of blood and guts. Maybe he has a thing about fluffy bunnies."
I think I'm glad X-COM didn't feature bunny mutilation, in hindsight. The cows were more than enough. I'd have loved an expansion which contained some of the other unused aliens, however. Modders, the gauntlet is thrown.
There are two more screens of new/old aliens on Gollop Games' site, which you should most certainly go eyeball if X-COM is one of 'your' games.
Also, is that a... Lemming on the lower left? What a crossover that would have been, eh?