10 Best Star Trek Crossover Episodes

Now yes, the academics amongst you will pipe up here and insist this isn't a crossover episode. It's actually an existing character being added to another series and that's not the same thing but, honestly, I can't say this enough, please have a day off.

As far as I'm concerned (and in the land of online content, the man with the publish button is Q) Worf wasn't a cast member of Deep Space Nine until he put on that nice new red uniform. All the time he spent in that classic yellow number, he was on loan from The Next Generation and, thus, this is a crossover.

Long-story-short here, Ben Sisko has a problem with The Klingons on the station and, short of options, reasons that the only person who can deal with them is, obviously, another Klingon. He recruits Worf for a temporary assignment ahead of his retirement from Starfleet, and so many skulls need cracked he decides to stay on full time.

Plus, this contains quite easily the single greatest space battle seen in Star Trek up to this point, as dozens of Klingon ships take on an astonishingly well-armed DS9.