Some of these past crossovers could be use a bit of a touch up if not a different idea for a story.
TMNT vs Mighty Morphing Power Rangers: Yes, this is a crossover that did exist. Two of the most popular shows during the 90s had met face to face, though it was done more with the live action shows. There might possibly be a sensible story here if given the right motive and/or plot device. For instance, Rita Repulsa & Lord Drakkon could be looking for new allies and enlist Shredder and Krang to assist them in defeating the Power Rangers with some enhancements. Thus in need of assistance, said heroes can call upon the heroes-in-a-half-shell to aid them with upgrades of their own. Plus, who thinks it might be epic but a little silly if the Megazord fought against a giant Krang and\or Shredder?
Batman/Superman vs Alien/Predator: the stories for this can be different than what the original comic had. The story could be that the Super Predators from 'Predators' would come to Earth to hunt for Superman and once captured, it's up to the Caped Crusader to track them down and liberate the Man of Steel.