Crossover with old episodes. During '90s Trek, there was the occasional use of crossovers - the Enterprise-D goes to Deep Space Nine, Riker shows up on Voyager, Riker (Thomas) shows up on Deep Space Nine, Riker shows up on the NX-01 ... and some other non-Riker examples. Then a crossover happened that blew fans' minds - the crew of DS9 visits station K-9 and the NCC-1701 in "Trials and Tribble-ations." Now in the 21st Century, what crossovers with older episodes do we wish other series' crews could visit? Should we give the "Star Trek: Enterprise" crew their revenge, and allow them to take over another show's episode? Could the crew of the USS Discovery visit their future or past, depending on which season we use? Let us know what Trek episode should be visited by another show's characters to make it even better.