Mirror Odo's uniform sports a belt and turtle neck, which Rene Auberjonois liked so much that he began using it in his regular series Odo uniform as well, starting in Season 3.
Unlike the regular Odo, who finds weapons distasteful, Mirror Odo carries a Bajoran phaser pistol.
For the milk bath sequence, the crew made sure that the bath was nice and hot for Nana Visitor, and even put a few drops of orange oil on it, so the water had a nice smell and even soften her skin. But during rehearsals, she felt the cones hiding her nudity, started to pop off, so she asked her makeup artist what takes the glue off the cones, and her answer was 'orange oil'.
Writer Robert Hewitt Wolfe wrote the fall of the Terran Empire into the script as an analogy for the fall of the Roman Empire to barbarians and the Chinese Dynasty to the Mongols. He also wanted to illustrate that if an Empire is as brutal as the Terran Empire was in Mirror, Mirror (1967), there were probably reasons why it was so brutal and he wished to convey the message that, in such circumstances, one cannot change things overnight, and even the actions of Captain Kirk can have severe consequences.
In the mirror universe, Quark tells Garak he is "a simple bartender" when accused of running illegal operations. This is a joke based on Garak's usual claim that he is just "a simple tailor", in response to the suggestion that he is a spy.