system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Is Q aware of the mirror universe?
gpt
He most likely is aware that it exists (since he's basically omniscient and can travel anywhere in the multiverse with a snap of his fingers) but doesn't visit it because he finds it repellent. 

His entire motivation to interact with humanity (and particularly Jean-Luc Picard) in the main timeline is to poke us and prod us along a certain path which will ultimately lead to us becoming morally superior beings that evolve into a species very much like the Q themselves. 

He chose Picard as his main "test subject" because Picard has a strong moral code backed by deeply-held beliefs and philosophies. Q wishes to test how firm Picard's morals are, and to put him in situations where he has to learn certain "truths" that Q believes humanity needs to accept in order to continue their journey down the path he wants them to go.

The Mirror Universe is the antithesis of what Q wants humanity to become. Instead of morally superior beings, humans in that universe are crabs in a bucket, constantly pulling each other down simply for the sake of chasing personal power and fulfilling their basest animal urges, without any concern for who they hurt in the process. 

Q can't set that version of humanity on the path to becoming like the Q. It would be disastrous for the multiverse. Therefore there's no need for him to interact with them, and at any rate, they wouldn't be any fun for him to play with.