What would Star Wars be without a bunch of different aliens? It's been the staple of pretty much every environmental wide-shot in the movies. With Rogue One's retro appeal (and place in the timeline), it fits right in and brings a couple of new creatures into the mix.
In-line with the classic films and unlike the prequels, the effects on all the new aliens are mostly physical instead of CGI. Even George Lucas visited the set and had nothing but good things and self-depreciating humor to say.
For a close look at how the aliens appear in the film, see the video below. What's your favorite one shown here?:
