Homestuck or Steven Universe, but space travel and society work the way they do in Treasure Planet or the Larklight series.
A Leverage AU where Jim Sterling, agent of INTERPOL, is replaced by Jim Sterling, Video Game Journalist and Internet Shouty Man.
Narnia, but Lucy and Susan are St. Trinian's girls and thus well versed in all manner of hooliganry and delinquency by the time they are unleashed upon an unsuspecting realm.
The Crystal Gems as the hosts of The Last Podcast On The Left, which is an injoke-turned-actual-AU some friends and I came up with solely because Amethyst is so obviously Henry Zebrowski. Pearl and Garnet are Marcus Parks and Ben Kissel, respectively, and for a $25 monthly Patreon donation, Pearl Parks will send you a gem shard from the war. Steven is Travis Morningstar, and yes, Amethyst Zebrowski DOES insist on calling him Titties. Jasper is Jackie Zebrowski. Peridot is Natalie Jean. Bismuth is Carolina Hidalgo and the only time Pearl willingly eats is when she and Bismuth are having pickle dinner.
Actually, you know what, I said this and I realized one better: I want to see the Citadel's reaction to the Radch and their AI warships, my god. There's so much room for fuckery by mashing any warping travel scifi properties together.
Desire to combine live-action Disney works and Powerpuff Girls in our megacrossover has resulted in friend and I writing some scenes of Camp Gangreen Lake. Hey, we needed some more teenage delinquents to fill the place up!
the sad turtlecat goblins in the Rankin-Bass Return of the King singing Where There's A Whip There's A Way but instead of the fantasy armor they're in Vietnam-era US Army uniforms with like peace signs hanging next to their dogtags or on their helmets and shit
Sonic Forces honestly screams to be made into some kind of a crossover. Maybe TF? IDW has the rights to both.
saw this post and now I am 100% convinced that Coraline is canon within the world of The Magnus Archives and the Other Mother is a monster of the Stranger
This wouldn't exactly be a crossover but I love the idea of the Holes boys watching and riffing Battlefield Earth, because the aliens in that enslave the humans for the purposes of mining gold, and I figure the boys would find the idea of the Warden and Mr Sir magically beaming Euclidean geometry into their brains when all they needed to know was "dig here" hilarious.
Also consider: sollux as an aburame Another path, Biju are contained by limebloods! Meenah couldn't completely cull them because of this, so instead generated centuries of distrust and isolated them to their "jobs" as jinchuurki