Three of the main characters were the same actor, and yet there are shots with all of them in the same scene. When I saw this as a young adult I didn’t even notice that Mike Myers was playing three roles and was genuinely dumbfounded years later when I found out.
How did they do those scenes so seamlessly?
Red Dwarf was doing same actor multiple roles for a long long time. There are many episodes to check out, but one of the best examples is Stasis Leak (3 of each character on screen), another good example is Me2 (Rimmer and Rimmer). They were doing this in 1988.