A star trek crossover: The unification spell of season 4 won't work for some poorly explained reason and as a result the crew of the Enterprise is sent back to fix the time-line. Not being familiar with magic, they rig up a subspace something(tranceiver, gadget, thingamagig) and inject Giles, Buffy, Willow, and Xander with borg nanoprobes creating a small borg collective that enjoys off-beat humor and is one quarter british. They kill Adam as a collective, but the enterprise crew is unable to remove the nanoprobes. As a consequence, Buffy(with the full approval of the other three) rips Data's arms off and beats Captain Picard, Geordie and Reg to death with them(although the fight is pretty spectacular, an armless android is still pretty formidable.). Eventually Data is subdued and imprisoned in Buffy's basement. Having gone at least partially insane, the newly born collective decides to assimilate Sunnydale.
On the enterprise, the crew is reeling from the death of a significant fraction of the senior staff. It is clear that the Scooborgs must be stopped, but historical records indicate that that might not be wise. In a few years though, they could level the entire city, should they want/need to, but no one wants to wait that long. Riker decides to flip a coin, heads he obliterates Sunnydale and all of it's inconvenient citizens, tails he has a snack. The coin-flip becomes moot however, because unbeknownst to the crew, Dr. Beverly Crusher was turned while she was a part of the away team. Using her astonishing ability to blend into the background by being totally irrelevant she had gone off somewhere(the bathroom maybe? Who cares?) and had been killed and turned. Her return was equally ignored. Once aboard, she started to 'recruit' others, starting with Deanna. And so, just as Riker is about to flip the coin he is distracted by some breasts and killed in the ready room.
Back in Sunnydale, Data is working on escaping, the chains are strong enough to hold his legs, but he believes given enough time he can work them loose of the wall and attempt to remedy the situation. Above ground, Sunnydale's assimilation progresses. The collective decides that Willow should teleport to the Enterprise to start assimilating it. Willow materializes in the conference room and alarms start to go off. Vampire Tasha Yar(who didn't die in order that the next scene could happen) responds to the intruder alert(she may be a vampire, but her job is still her job). She storms into the conference room, and then Borg-Willow and Vamp-Tasha get it on.
Data has managed to free one of his legs and he believes that he may yet succeed in saving the day, but he is concerned that he will be unable to defeat the manifold enemies that await. A heretofore unknown program created by Dr. Sung activates and Data finds himself in a training room(matrix anyone?) and a digital Dr. Sung gives him intensive training in no-armed fighting. Data yanks his other leg free while deep drumming music is heard somewhere in the background.("I am iron-man" is heard)
Meanwhile, everyone on board the enterprise is dead, except Willow(she and Tasha are still going at it). Two vampire factions have developed; one led by Deanna Troi, the other led by Chief O'Brien... who hate each-other. They agree to seperate the ship, the Chief manages to pawn off the saucer-section on the Councillor, keeping the awesomeness of the star-drive for his side.
Data delivers an incredible armless beatdown on most of The Scoobs, killing Giles and Xander, before being felled by Buffy, who feels the satisfaction of yet another victory and raises her arms into the air, triumphant. This doesn't last, because the saucer-section of the enterprise(inadequately piloted by Vamp-Wesley-Crusher) crashes into and obliterates the entire town, killing everyone and everything.
And that's how a the vampire-ship Enterprise ended up wreaking bloody havoc for the rest of time.