Invader Zim: The Most Horrible X-Mas Ever (2002)
Invader Zim is a weird show. It's one I really wanted to like, and kinda did like from time to time, but I generally don't enjoy watching it. If you missed it (it's obscure for some), it's an animated series with a twisted aesthetic, about an alien who is trying, and failing, to take over the Earth. Some episodes were disturbingly brilliant, others just disturbing.
This was the last episode that aired in its original run (more episodes were finished but not aired for several years after the show was canceled) and actually given the “Two Million Years in the Future” frame scenes, it almost works as a weird ending. Zim discovers that humans await the return of “Santa” to save them, or something, and Zim decides to play upon their gullibility, disguise himself as Santa, and enslave all the humans. It comes fairly close to working.
This episode is mostly worth watching for the ending, which is pretty fantastic, but getting there involves sitting through a lot of boring and/or unfunny scenes. This show was pretty uneven at the best of times. Of course, I don't often like gross-out humor or humor based on everyone being idiots, so your mileage may vary.
I did really like the end, and if you're curious enough to see for yourself, and in the mood for some humor black as coal, Invader Zim is streaming on Netflix Instant. The Christmas episode is the last one on the page.