Ok, so an explanation for the people who don’t understand or weren’t there to know:
Back in 2014 at the worlds championship (the highest level of competitive pokemon, with the best of the best), there were a few pokemon who were dominant in the meta of the time with the restrictions (x and y just came out, championship rules means teams can only be made of pokemon found in x and y, aka the regional dex). At the time, there were planty of heavy hitters and clearly dominant pokemon, such as:
Mega Kangaskahn: strong as hell and bulky, ability lets it hit twice so almost impossible to take hits from and hit back as hard.
Garchomp, Hydreigon, Tyranitar (all 3 seen above), and Salamence: pseudo-legendaries (600 base stat pokemon, way above average) with huge attacking stats and either the speed or bulk to take on almost everything in front of them.
Rotom and it’s forms: high power with few weaknesses and an immunity to ground, tought to kill and can reek havoc on a team with statuses and high power moves.
Gardevoir and Amoonguss: great support mons, both tough to kill and make your opponents life hell.
Mega Mawile and Charizard: both megas hit hard, and can use a mix of nuke-level power and interesting support (priority and weather setting) to make an enemy team go to shit fast.
So all of these mons, and most people saw these pretty clearly strong pokemon and ran with them, tried and true sets of pokemon and all that. And yet one person wanted to break the mold, and saw a way to do so, and that person was that Sejun Park.
Now there were some weaknesses with the common meta of pokemon: not many resistences to water or dark, a majority are physical attackers, and a good few more defensive pokemon rely on abilities. That’s where the 1st unique change shows up: Mega Gyarados. Upon switching in, it’s flying typing gives it an immunity to ground attacks, and it’s ability intimidate lowers the attack of opposing pokemon. Then, it can mega evolve, with it gaining the dark typing (becoming water/dark), and both a good stat boost (better defences (which were already good) and a LUDICROUSLY high attack). However, there were issues: the frequency of Tyranitar and the Rotoms meant common super efective moves and danger switching in and out. Additionally, coverage fighting attacks made actually mega evolving dangerous, risking a high power attack punching a hole in your best attacker.
To fix these issues, 2 pokemon helped:
1. Gothitelle. It’s ability, shadow tag, make it so opponents can’t switch. Combine this with it’s good defences and special attack and status moves means that any pokemon in a bad situation on the enemy team is as good as dead, and a bad situation for an ally pokemon can switch out while the enemy can’t do shit. And of course, the other pokemon was:
2. Pachirisu. Now those who don’t know, pachirisu is what is known as a “pikachu clone”, a set of pokemon (emolga, pachirisu, plussle and minun, etc) with lower than average (for competitive) base stats. Now why was pachirisu so good? Simple: it matched PERFECTLY with gyarados. It’s suprisingly good defenses means it’s tougher to KO than expected, has high speed, it’s move Super Fang always does half the health of an opponent so no need to invest in attack and bypasses higher defenses on an opponent, nuzzle to chip a bit of health and paralyse an opponent (halfs speed and has a chance to make the opponent not attack during a turn), and most importantly, Follow Me. Follow me (and rage powder, same mechanics) redirect an opponent’s moves to itself, allowing a less health pokemon, or one about to get hit by a super effective move, to stay healthy. Mix that with it’s ability Volt Absorb (heals user when hit by an electric attack) and electric attacks that would cripple Gyarados instead do nothing but heal Pachirisu instead. On top of all of that, it had enough defenses to take attacks from even the afformentioned pseudo-legendaries, hits even the likes of mega gyarados or gothitelle would be devestated by. Plus it’s health restoring berry, it was a bastard to kill, crippled whole team that didn’t expect it (aka all of them), and set gyarados up to sweep entire games.
Add some other hard hitting mons as back up, and your mix of support redirecting pachirisu that no one expected to see, supporting trapper gothitelle to trap and screw over opponents while keeping yoir team safe, and mega gyarados nuking the opposition while also helping to shut down opposing threats with its mix of abilities, and you have a powerful as hell, albeit somewhat unorthodox team. But it worked. How well did it work?
It made it to the grand finals.
AND WON.
To this day, Pachirisu, thanks to this legendary team, has more championship wins than a majority of legendaries and starters.
If you want a better understanding and more in-depth information on all this, I reccomend looking at this video by WolfeyVGC, a world champion in competetive pokemon, and one of the best sources of information on competetive pokemon: