Mirror, Mirror on the wall...
it's my favourite episode of them all. Speaking of the Parallel "Evil" Universe, I am now watching bearded Spock and the rest of the alternate gang. This was the coolest thing I'd ever seen to date back then with evil versions of the Enterprise crew.
This has led to all kinds of storylines to future ST tv shows. South Park gave Cartman a beard which turned his counterpart into a "good" kid. And I just discovered that there was a band called "Spock's beard" created in 1992.
As proof that this is indeed a parallel universe, Sulu hits on Uhura. As any true Trek fan is aware, women are the furthest thing from his mind.