10 Best Star Trek Crossover Episodes
1. Trials And Tribble-ations
Arguably Star Trek's most unsubtle, balls-out, look-everyone-it's-that-other-show! attempt at a crossover, and lo and behold it also just happens to be the best. Trials And Tribble-ations doesn't draft in some guest stars for some hokey plot contrivances, it straight-up sets an entire episode of DS9, in an episode of The Original Series.
In short, two suits from Starfleet's Temporal Investigations department arrive on the station to receive Sisko's report over a recent mission. He tells them that he and the rest of the Defiant's crew were flung back in time and, while there, prevented the assassination of James T. Kirk during the original Enterprise's fabled mission to the K-7 space station.
Donning the old uniforms and being digitally placed in scenes from the episode, it's supremely well put together from a technical perspective with a story that works as a loving ode to the show without ever veering into cheesy parody. Dax and Sisko interact with Kirk, Worf refuses to address why the Klingon's of the day look so different, and there's all manner of entertainment to be had with how much things have changed.
Plus, Tribbles!