When it comes to the Royal Rumble, it's technically an inter-gender match because it's open to all division, including Divas and there have been three so farnote Chyna in 1999 and 2000, Beth Phoenix in 2010, and Kharma in 2012. Since the winner is given a chance to challenge the current champion (in this case WWE World Heavyweight Champion), but there isn't a rule it has to be a guy. Haven't said that, if a diva enters and wins the Royal Rumble, she could in theory challenge the current champion, even if it's an inter-gender since the WWE Divas Championship, WWE Intercontinental Championship, nor WWE United States Championship is mention... it used to be the WWE Championship or World Heavyweight before it was unified.
One of the main rules of the Royal Rumble Match, for an entrant to be eliminated both feet have to touch the ground after being toss over the top rope. However, many wrestlers got around some loopholes.
One: Have to been seen by the referee in order for an elimination to count.
"Stone Cold" Steve Austin took advantage at the 1997 Rumble while the referees had to deal with Terry Funk and Mankind when Bret Hart eliminated him, but Austin got back into the ring because of the distraction and the ring announcers didn't have a say... the referees do.
Those won't aren't entrants can do this to just as long the referees don't see them. At the 1999, The Undertaker simply had the room darken in order to have TheAcolytes and Mideon to go get Mabel in order to turn him into Viscera.
Two: "Both" feet have to be on the ground in order to count. At the 1995 Royal Rumble, Shawn Michaels had one foot after being tossed over the top ropes by The British Bulldog but not the other one, which was still in the ring.
Three: The feet have to be on the mat to count as elimination, but there are no rules against any method to avoid elimination.
Landing and walking on the railing to the steel steps, like John Morrison did in 2011.
Hand walking… Kofi Kingston resorted to this in 2012, winning a Slammy for it. Then, bunny hopped on JBL's announcer chair in 2013, and then did a running jump from the barricade to the ring mat in 2014
Four: Top Rope only, through the ropes doesn't count. Many wrestlers had this happened and they were safe because of it.
Most famous example of this was in the 1999 Royal Rumble when both Steven Austin and Vince McMahon went through the ropes and returned later on, though the latter had help in hopes of keeping the former from return in order to have him eliminated since that can be happened if the wrestler isn't able to return. It didn’t work, as Austin was able to return by driving an ambulance while The Undertaker was taking Mable.
Hiding underneath the ring, provided you were tossed through the ropes, can help you avoid elimination just as long you'll be able to return. Jerry Lawler tried in 1996, only to be caught and later eliminated by another who's was threw through ropes and knew what to find Lawler.
Five: The only way to get a disqualification is going before your number. When your number is up after the ten-count, how you enter isn’t listed and you can enter the match in other ways.
Steve Austin did this at the 1998 Royal Rumble by going through the French Commentators when he was called.
Six: There are no rules on bringing in a weapon.
Mick Foley and Terry Funk did just that in 1998, although a chainsaw brought by the latter should've been banned note a referee did remove the chainsaw, much to the relief of Jerry Lawler while the former brought in trash cans and steel chairs, which are okay. Later on, Austin used his jacket.
Seven: One gimmick at a time, but there are no rules on multiple ones by the same person.
Foley took advantage of this in 1998 with his: Cactus Jack, Mankind, and Dude Love.
Eight: There wasn’t a rule about snakes in the Royal Rumble.
Nine: Speaking of which, size doesn't matter... much like Divas, those with dwarfism are ALSO ALLOWED... hence where Hornswoggle joined in 2011 and El Torito in 2014.
In a Ring of Fire Match, having a wrestler set on fire no longer will result in a win unlike its’ predecessor note Inferno Match, set in a ring surrounded by fire, but it can only be won by pinfall or submission. The fire is to prevent outside interference, but there’s no rules of any simply putting a fire-resistant blanket to create a path to allow it. The Wyatt Family members, Harper and Rowan, resorted to this to help Bray Wyatt be deal with Kane at SummerSlam 2013.
When it comes to a champion match, you can run across the ring upon the bell being ringed and stay underneath until the right moment; the match would still be valid. A certain leprechaun was able to get the cruiserweight by doing that at The Great American Bash in 2007!
Classic Professional Wrestling trope. The most obvious is the loophole that a title (usually) can't change hands unless the victory is 'clean'; if a heel were to, say, disqualify himself by hitting an opponent (restrained by his allies) in the groin with a foreign object while outside the ring over 10 seconds, he'd retain it. Then there's the classic No Holds Barred/Street Fight/Hardcore match, where there Ain't No Rules. Aside from 'win via pinfall or submission'.
As with so many other things, Eddie Guerrero was the master of this. While the ref was distracted, he would grab a chair, hit it against something to make a noise, throw it to his opponent, and then lay down. The ref would reach the logical conclusion and DQ his opponent. Ain't no rule against giving your opponent a weapon.
When it comes to men and women, it’s rare for a match between them these days. However, nothing says a woman can’t break up a fight or hitting a guy outside of a match. At the 1000th episode of Raw, Stephanie got around this when Paul Heyman started to trash talk about her children, and she let him have it. Triple H warned Heyman about this since he’s the father of Stephanie's children and he’s protective of them too.
When it comes to the Elimination Chamber Match, there is no rule that forbids one for a chance at any other Championship matches. Considering, this type of match is offered for those who failed to win a chance for a match up at WrestleMania via the Royal Rumble for a chance at another title match and the World and Heavyweight have been unified, there’s a chance to allow Intercontinental Championship or United States Championship to be offered this way, same goes with Divas.
At the 2014 Royal Rumble, John Cena learned there wasn’t going to be any outside interference or added stipulations but the match was going only to win by pinfall or submission, which The Authority promised. Unfortunately for Cena, he wasn't aware that rule was implied for the Authority including The Shield, which they did live up to their word, because they didn’t mention “who” would be that interference. This cost Cena the match when the The Wyatt Family showed up. The next, Triple H promised Cena and two others, Sheamus and Daniel Bryan, a chance to take part in the Elimination Chamber Match via 6-man tag team match against. However, Cena, Sheamus, Bryan got the last laugh because Triple H didn’t realized disqualification rule applied as the Wyatt Family did it again, costing the Shield the match.
Really, anything with Kofi Kingston will definitely have him use Loophole Abuse somehow. At the Wrestlemania XXX Andre the Giant Battle Royal, he was hurled over the ring post, with his feet landing on the bottom ring step, to avoid elimination.