I've been thinking a bit lately about the way franchises change over time as their fanbase ages. It seems like as the fans get older, they want to continue to have a main character in their favorite action-adventure series that they can relate to; if they're in their thirties, dealing with the challenges of mature relationships and child-rearing, then Spider-Man should too! They can't continue to identify with a young Spider-Man, and they certainly can't stop reading Spider-Man. Ergo, Spider-Man should change to be more like them. (Inevitably, the word "stagnation" gets thrown around in these discussions.)
But we older fans forget that younger fans age too. And if we want a darker, more "adult" take on our favorite characters, well...isn't it only logical that they will too? Let's go ahead and get to the grim and gritty take on the next generation of franchises now, and beat the rush, shall we?
Teenage Mutant Ninja Turtles: The Turtles are retired following the death of Shredder, but are forced out of retirement when Bebop and Rocksteady go on a brutal rampage that kills dozens of people. They follow the trail back to Baxter Stockman, who has gone insane, but he resurrects Shredder as a zombie Shredder who brutally tortures Splinter to death. The Turtles avenge their mentor by throwing Shredder into a wood chipper (see, irony! He's shredded!) only to find out, when they go after Stockman, that he's just a flunky for the true villain...April O'Neil! It turns out that Everything They Knew Was Wrong(tm), and O'Neil has been behind every villain they've ever fought. She did it all to further her stagnant journalistic career, including mutating the Turtles themselves (while pinning the blame on Shredder.) In the end, they kill her...but her body falls into the mutagenic ooze, setting up a potential sequel.
Mighty Morphin' Power Rangers: When Rita Repulsa's love potion wears off, Lord Zedd mercilessly slaughters her in full view of the audience, and begins his plan to destroy the Earth...starting with the Power Rangers. His new nanoscopic monsters infiltrate Alpha's systems, secretly turning the robot against Zordon. Alpha sabotages the Morphing Grid, robbing the Rangers of their powers, then traps the Pink Ranger in their headquarters and tortures her. Dying, the Pink Ranger sacrifices herself to detonate Alpha's anti-matter power core, destroying him, her, Zordon, and the HQ. The surviving Rangers, unable to access the Grid, steal a space shuttle and break into Zedd's moon base, stealing his own weapons and using them against them. After a bloody shooting war (in which Goldar kills two more Rangers before they put him down) the Rangers reveal that the battle was only a distraction--this was actually a suicide mission, and they armed every explosive in the base. The resulting explosion can be seen from Earth, where a young group of teenagers watches it. The light show gives them strange, mysterious powers...
Pokemon: It's a show about a little boy who runs around capturing wild animals, locking them up in a tiny cage, and then pitting them against other wild animals in brutal gladiatorial contests. Really, I don't think there's anything you could do to make this one darker if you tried.