"Black Saturday". In 1984, the then-burgeoning WWF had purchased Georgia Championship Wrestling, a popular yet struggling Southern-style promotion. Vince McMahon appeared in the opening segment of the July 14 edition of World Championship Wrestling, GCW's flagship nationally televised program, to deliver a show that mostly had material that had ran already run on other WWF programs. Complaints from the GCW fanbase lead TBS to give Bill Watts and Ole Anderson's promotions slots on their schedule in tandem with WCW, and the WWF was ultimately forced to sell the TBS timeslot to Jim Crockett, whose promotion would become WCW.
The 05/27/96 episode of WCW Monday Nitro featured the shocking return of Scott Hall and the beginning of a landmark storyline in the industry, one that would effectively swing the balance of power towards WCW (legitimizing the company in the eyes of the mainstream public) and keep it there until WWE came back with a vengeance a couple of years later.
The 07/29/96 episode of WCW Monday Nitro opens with the great announcement, tonight we have two title matches: The Giant and Arn Anderson for the WCW World Heavyweight Championship and Rey Mysterio Jr and Eddie Guerrero for the Cruiserweight Title. That alone is awesome, but after the opening match Ric Flair's theme starts and it's Ric Flair and two of the Four Horseman against Sting, Macho Man and Lex Luger. Man, this show is going to be awesome. I mean, seriously SERIOUSLY awesome. In the middle of the match Stinger is getting the crap beaten out of him, and it's looking like it could be comeback time. But then Jimmy Hart runs into the arena screaming "Get back stage!" and we find Scott Hall and Kevin Nash tearing shit up and beating Arn Anderson and Marcus "Buff" Bagwell up with baseball bats. Then Rey Mysterio comes in only to get picked up and thrown into the side of a trailer HEAD FIRST and lies on the concrete motionless. EVERYBODY runs backstage and there is chaos, wrestlers in agony and people screaming for help. Then it hits you: there are going to be no title matches tonight. The nWo have hospitalized the competitors. Everything is ruined and the entire show is thrown into chaos. Bobby Heenan doesn't feel safe and walks out on the commentary team. Before this the nWo were nothing but Hulk Hogan and his buddies talking shit and pulling silly stunts. This episode, shit got real.
Uncensored 1997. The nWo win the main event match and what amounts to basically a perpetual "Money in the Bank"-type clause for all WCW titles. The REAL development, however, is Sting ending months of speculation on whose side is he on by kicking the nWo's collective asses, striking the first real blow against the renegade group.
The 04/13/98 episode of Raw had the company teasing a match between "Stone Cold" Steve Austin and Vince McMahon, leading to the creation of their own Wham storyline which not only broke WCW's 84-week-long winning streak in the ratings war and swung the momentum right back in the WWE's favor, but kept it there permanently after WCW went bust.
The 03/26/01 episodes of WCW Monday Nitro and Raw, in which the last Nitro segment ever was a Raw simulcast. Nitro and Raw both opened with Vince McMahon gloating about his purchase of WCW. WCW was known to be in financial turmoil at the time and there were (mostly unsubstantiated) rumors that McMahon was working to purchase it, but the deal was only announced the weekend before the broadcast. The simulcast segment also culminated in a huge (kayfabe) swerve involving Shane McMahon, as if Vince McMahon buying out his bitter rival wasn't huge enough for one night. To say nothing was the same in pro wrestling after this night would be a dreadful understatement.
And then a few months later, when ECW showed up...
Championship Wrestling from Florida, October 1982. Kevin Sullivan has been working Tweener for months while defending his NWA Florida Heavyweight Title. Meanwhile Jake Roberts has been bragging about how a "Nivek Navillus" had paid him good money to beat up Barry Windham. Sullivan defends the title successfully against Windham. After the match, Sullivan rips Windham's nose guard off, and kicks him in the head. The following week, he shows up with an "X" on his forehead and ranting and raving. Announcer Gordon Solie explains that "Nivek Navillus" is "Kevin Sullivan" spelled backwards. Thus begins his whole epic run as a "Satanic" heel.