Treehouse of Horror XXI (Season 22; Nov. 7, 2010)
Amazon; Disney+; Halloween Specials Wiki; Halloween Wiki; IMDb; Simpsons Wiki; TV Tropes; Wikipedia
Intro: It begins with Bart pranking Homer, but then switches to Professor Frink fastforwarding through the episode. Then there's an opening credits spoof of The Office, but with monsters. It was okay.
War and Pieces: In a parody of Jumanji, Marge forces Bart and Milhouse to play a board game instead of the violent video game they were playing. They find one called "Satan's Path," and as soon as they start playing it, all the other games come to life and wreak havoc throughout town. That's also what appears to be a random Titanic allusion. It was all reasonably amusing.
Master and Cadaver: In a parody of Dead Calm, Homer and Marge are on a second honeymoon on a boat out at sea. They rescue a man named Roger (Hugh Laurie) from a rowboat, and Homer becomes jealous of him. But he might be a killer. Or not. The best part is that the very end has a totally random allusion to A Clockwork Orange.
tweenlight: In a parody of Twilight, Lisa dates a vampire named Edmund (Daniel Radcliffe). There are plenty of decent gags. It's probably the best segment of the episode.