Google's AR Stickers is a new feature that is currently only officially available for 1st and 2nd gen Pixel phones. The feature allows you to overlay AR images over the image your viewfinder is currently on. There are all kinds of fun stickers from Star Wars to Stranger Things and more. The feature can now be installed on some rooted phones like the Nexus 6P, OnePlus 3, and Xiaomi Mi 5. The full instructions an be found at the link below.
via XDA