6. Daleks Invade The Quidditch World Cup (Doctor Who/Harry Potter)
OK, so this one was just begging to happen, since Tenth Doctor star David Tennant has actually appeared in the Harry Potter universe as Barty Crouch Jr. There's so many crossover clips to use, it'd just be plain rude not to! The Quidditch World Cup is one of the most anticipated events in the wizarding calendar but the festivities were cut short during Goblet of Fire when the attendees were attacked by an army of dreaded Death Eaters. If they thought that was bad, though, just imagine how quickly things would've escalated if it had been the almighty Daleks unleashing their tyranny of terror instead. The Daleks or the Death Eaters. It's hard to say for sure which one is worse (though you wouldn't want to come across either of them in a dark alley!) but thankfully, on this instance, there's the arrival of a familiar face to help save the day. Ahem to that!