Superheroes with two origins

Definitely Skylark. I remember reading that as a teenager and snickering, “Yeah, okay.”

Daredevil, for the first fifteen years of his publication, got his radar sense and expanded senses from getting bitten by a radioactive truck. After Frank Miller took over, it was established that he had been trained by a hardcore ninja.

Nick Fury (the elder) has had numerous new origins and upgrades. He was an exceptionally talented army Ranger, then a CIA agent recruited to run SHIELD, then he got the Infinity Formula, then he was retconned as the Man on the Wall, and now he’s the Watcher’s agent. I think they’re just keeping his trademark alive until Sam Jackson’s contract expires.

Marvelman had his faux-Captain Marvel origin, then his Alan Moore origin, and he’s about to be foisted on the Marvel Universe.

Thread winner, right there.

In at least one version of the canon, wasn’t it the same accident that led to Daredevil and the Teenage Mutant Ninja Turtles?

yes. That was in the original comic book

Yes. Matt taught by Stick fights the Hand; the TMNT taught by Splinter fight the Foot clan