The "steel cage" used in Steel Cage Matches transformed over time from something that kids would probably enjoy climbing at Chuck E. Cheese to, well, an actual steel cage. However, the steel cage itself is lighter and softer, as the first cage matches in pro wrestling used chicken wire.
Lucha Libre Internacional was marginally but still noticeably heavier in tone than EMLL, which it broke away from, one of it's most famous angles, which in turn lead to the tercias match being associated with Mexican wrestling, was started by heart attack causing Fallen Angels, who formerly were El Signo(whose gimmick immediately before this was having blond hair and getting it shaved off), El Texano (formerly a cowboy) and Negro Navarro, (the only one with a remotely supernatural or worrying gimmick, which was simply being a fanboy of Black Shadow)
EMLL\CMLL later had two heavier, edgier breakaways in AAA and Perros Del Mal Producciones. Even more in line with the trope, PDM was originally supposed to be a spinoff\sister promotion. AAA itself would get a heavier, edgier spinoff called Lucha Underground.
Over the years, Scott Levy turned from the effeminate Scotty Flamingo into the brooding, psychopathic Raven
ECW from 1996 onward was considered a more darker and edgier professional wrestling organization when compared to other organizations like WWE or WCW back in the day as ECW's angles took a more mature approach over the cartoony "storylines" WWF and WCW were using. ECW had actively based itself on older, more serious times in wrestling as well as on garbage wrestling promotions such as FMW.
The WWF'sAttitude Era gained so much attention because it was so much Darker And Edgier than the days of Superhero-like wrestlers like Hulk Hogan, the fact that much of the new flavor was imported directly from ECW aside. It could be argued that this was inspired by WCW's taking its two main wrestlers, Hulk Hogan and Sting, and transforming them overnight. The Sting gimmick morphed from a brightly colored California super-surfer to a grim, vengeful Nineties Anti-Hero, a wrestling version of The Crow. Hulk Hogan became "Hollywood Hogan", an all-powerful gangster with a Hollywood-sized ego. This inspired WWF to change their direction as well as ECW's gaining momentum.
The Undertaker and his Ministry of Darkness gimmick. Undertaker has always been 'dark' so to speak, but when the Ministry came into existence he become a full blown villain, using creepy religious symbolism, crucifying opponents, abducting women, employing a cult of other wrestlers to do his bidding, the whole nine yards. He became less of a wrestling villain and more of something out of a comic book.
Shane Helms' original Superhero gimmick "The Hurricane," seemingly imposed on him in 2001 when he came in from WCW as a joke to amuse the writers, but, Helms' talent, charisma and enthusiasm got the character over with the fans. It helped that Helms actually has a genuine love for comic books. When he revived the character years later just before his departure from WWE, he attempted somewhat to reimagine Hurricane as a grim, silent, Dark Is Not Evil avenger.
Try going from Chikara to CZW like The Kings Of Wrestling, though Chris Hero didn't fully drop the superhero stint and become knockout obsessed until his run in ROH, it was still in CZW where he got a messianic complex. It's often averted though, with The Osirian Portal being just as silly in CZW as in Chikara.
Unlike WWE, TNA had more violence, blood, and profanity and was rated TV-14. It's also been viewed as Incompetence, Inc..
Interestingly, while WWE's PG era was initially exactly that, with relatively clean violence and little profanity, it's now gotten more than a bit edgier, the violence is more brutal, the language is dirtier and more frequent, and such Anti Heroes as CM Punk and Randy Orton are starting to become the norm again for faces. Add to that the returns of wrestlers from the Attitude Era like "Stone Cold" Steve Austin and The Rock, and it could very well be only a matter of time before WWE goes back to TV-14. Funnily enough, WWE initially started out as PG before transitioning to the Attitude Era, and then back to PG before starting to get edgier again.
In his WWE career, CM Punk has continued to become grittier and more visually dark, even when making a Heel–Face Turn. However he's much more on the "softer" side compared to his runs in IWA Mid-South, Full Impact Pro or Ring of Honor.
Chris Jericho's creepy video with the children before he returned to compete in the Royal Rumble, lose, and then face CM Punk (then face) at WrestleMania, which had been his plan all along.
With the family friendly + occasional Parental Bonus formula PG-WWE has established with its characters and storylines, the backwoods cult of The Wyatt Family comes off like an Attitude Era gimmick that got off at the wrong stop on a time machine. It has minor shades of the Ministry of Darkness except that it's a lot earthier and slightly less over-the-top, coming across a lot more like a cult you could very well run across in Real Life if you got lost in the wrong area. Bray, unlike The Undertaker, isn't so much a supernatural being, but he is a man that fully believes himself to be some sort of god, and that arguably makes him even scarier.
Bam Bam Bigelow debuted in the WWF in 1987 as a Gentle Giant of sorts, an agile, seemingly fun-loving big man who spurned all the heel managers bidding for his services in favor of the babyface Oliver Humperdink. He would leave the WWF a year later, and in 1992 he returned with the same Bald of Awesome hairdo, the same ring get-up, but with a heel persona and a slow, dark, ominous ring theme that contrasted to the happy sax music he entered to in 1987-88.