10 Best Star Trek Crossover Episodes

10. Through The Looking Glass

We start with Through The Looking Glass because it might be considered something of a contentious entry. Where the rest of this list has the crossover element front and centre in its story, what we have here is a bottle episode that included a prominent (but not crucial) role, for a star of another Trek. Specifically, Tim Russ as Tuvok.

However, being a Mirror Universe episode, it's got enough of a fresh feeling about it merit inclusion and it's just a fantastic episode in its own right anyway so, here we are.

Kidnapped from DS9 in the opening moments, Ben Sisko is recruited by the Mirror Universe O'Brien to play the role of freedom fighter for the Terran Rebels. His mission; convince the Mirror-version of his late wife to defect to their side or, as Smiley here very delicately puts it, watch her die for a second time.

He has quite the little adventure, too. Socking Bashir right in his whiney moy, and hopping on the good foot to do the bad thing with both Dax and Kira. Not to cancel myself here but this is Mirror Universe evil Nerys and yeah, absolutely fair play on that one.

Oh, and Tuvok's there too!