This is pretty cool. Watch the video embedded in this tweet:
iPhoneXで顔だけ光学迷彩っぽくなるやつできた pic.twitter.com/aPXJcHi8Y4— のしぷ (@noshipu) December 27, 2017
The developer built an app that runs on the iPhone X and uses the face mesh to render your face invisible. A neat trick. Not sure how useful this is, but A for effort.