I’m uh...curious about your reasoning behind all these
OK.
Dexter's Laboratory/The Flash: Barry is a forensic scientist and his powers came from a lab accident. He's one smart cookie.
Johnny Bravo/Wonder Woman: Cause Johnny is always stalking women
Powerpuff Girls/Super Sons: Cause there already was a Powerpuff Girls/Teen Titans crossover in Teen Titans Go and Super Sons is a more prominent new team of younger heroes. Plus 3 and 2 is a much better number for a team up then 3 and 5.
Ed, Edd n Eddy/Batman: Batman's the world's greatest detective and Eddy is the world's greatest con artist.
Courage the Cowardly Dog: John Constantine: OK. Do I really need to explain this one?
Samurai Jack/Booster Gold: Jack is a samurai trapped in the future, Booster does time travel all the time.
Codename: Kids Next Door/Suicide Squad: Two teams of off the books paramilitary squads with eccentric weaponry who go on secret missions.
The Grim Adventures of Billy and Mandy/Etrigan the Demon: A demon bound to two mortals and a mortal bound to a demon.
Evil Con Carne/Legion of Doom: Con Carne is all about poking fun at supervillain tropes so put him with DC's team of supervillains.
Foster's Home for Imaginary Friends/Sandman: Sandman is the lord of dreams, Imaginary Friends are MADE of dreams.
Ben 10/Shazam: Kids who gain the ability to turn into superpowerd heroes. Ben has 10 aliens, Shazam gets the power of 6 gods.
Chowder/Matter-Eater Lad: The only DC hero who has anything to do with eating and is also considered a joke by many, perfect for a show as humor-centric as Chowder.
Generator Rex/Blue Beetle: Hispanic teenagers with the power to form weapons from their bodies.
Adventure Time/Kamandi: The stories of two kids who are the last human alive in a post apocalyptic world of strange anthropomorphic creatures (food for AT and animals for Kamandi) in their respective universes.
Regular Show/Darkseid: Accidentally discovering the Anti-Life Equation and having to fight Darkseid is totally in line with the kinds of things that happen to Mordecai and Rigby.
Steven Universe/Green Lantern: Magical multicolored rocks from outer space powered by emotions.