Face the Faceless in XCOM 2
With the advent of alien control of Earth, our stellar overlords have been hard at work making sure any attempt to retake control of the planet would be as difficult as possible. Thus, the development of the Faceless was born. Though masquerading as your average, everyday human, these monstrosities transform into angry beasts well over a story tall once provoked. With the increased size comes increased danger, combat prowess, and overall strength.
This means that in citizen rescue missions, which are sure to make a return, you have no idea if you're going to suddenly come up to a Faceless, and start losing squad members left and right. It would appear as though there's no way to tell (at their onset, anyway) if a human is actually a human, or a Faceless instead.
XCOM 2 releases February 5th, 2016 for all computer platforms.