A surprsingly large amount of Doctor Who is still practical effects, though they now tend to fluff them out a bit with minor CGI. So the slugs from "Dot and Bubble" were practical but some of their movements were computer generated.

The Time Window from this week was an actual set, rather than a computer generated background

As was the facial prosthetics for THOSE characters (which instantly jump to some of the creepiest the show has done in a very long time)