In my head I was thinking more along the line of Mutations for the Bugs and Augmentations for the Bots. It would be cool to face a variant of the Charger that can jump or fly a short distance, or a machine weaker to small arms fire due to some kinetically-based shield that grows stronger the harder the weapons hit. Based on events though. I'm not sure this is a good game for enemies like this to show up randomly, even rarely.