The Simpsons: Every Crossover Episode Ranked - From Worst To Best
3. The X-Files
If Mulder in a boudoir photo on his FBI badge doesn't disturb you, well little will.
The appearance of Mulder and Scully - David Duchovny and Gillian Anderson, right in the prime of The X-Files - was heavily promoted by Fox, and led to something of a classic episode in the series. It all went down in season ten's The Springfield Files, and revolved around a mysterious, alien-like figure that Homer claims to have seen in the woods one night. While few seem to believe Homer, Mulder and Scully wind up on the case - and eventually, it's learned that the "alien" is actually Mr. Burns, suffering side effects from longevity treatments.
The outing also features the late Leonard Nimoy in a guest spot, and overall, it's one of the better crossovers. In fact, in retrospect it's much better than a more canon crossover X-Files episode, X-Cops, which saw COPS cross over onto The X-Files. That also had plenty of laughs, but those were sadly unintentional. The Springfield Files, meanwhile, gets points for combining FOX's two biggest hits at their peak.