One trend that I have noticed in rating battles is players relying on the best numbers instead of a strategy that can secure a win. While I do find some players who have pretty interesting tactics and strategies, the majority are all just "hit them with the hardest moves you can." Brute force can work in many games, but not in Pokemon. One reason are abilities.
I have been playing around with a Sableye and Klefki lead, both with prankster, giving them first move on status abilities. Loki, my Sableye, is a tough nut to crack as it is. He's highly underrated and his small form is misleading. With EVs evenly spread in both defenses and HP he has a lot of bulk for something so tiny, but most of all, only one weakness and several immunities.
But his move set is the key, same with the Klefki, they are 3 status moves and one damage move each. One of the pair alone will neuter most heavy damage causing opponents, but the two combined will reduce all the biggest, most powerful, pokemon into dead weight. Loki burns the opponents who pose the biggest threat, taunts other status users, restores damage he takes on his own. The damage move he has .... foul play. Foul play uses the target's attack stat for the damage, which is devastating to the heavy attackers.
Klefki has both screens and drain kiss, the fourth move I have yet settled into and it keeps changing at this time. If the Klefki sets up both screens, I usually start with reflect because most teams I have faced are mostly physical attackers, then all damage my team receives is halved. Even fire damage from a mega Charizard to my Klefki is only an inconvenience.
Leading with them both is kind of a cheap trick, but it's loads of fun, only because most opponents I face have almost nothing but heavy damage moves. Many of the overlooked, underrated, and generally scoffed at pokemon have benefits like Klefki and Sableye, their abilities and move pools can disrupt an opponent's primary strategy very easily. I also notice a lot of players running damage calculations, expecting the opponent to be as predictable as they are. This is cool, because when you run damage calculations it makes you even more predictable and anything I do will disrupt your tactics without much bother.
Now, the truly unusual pokemon I often run with, Galvantula. His name is Tallit, and yes, he's a glass cannon, but one of the more buff ones. Often my Gavlantula manages to take down two or three opponents before getting squished, which surprised me as I only expect him to take down one. The reason for this are the EV spreads. Putting maxed EVs in anything is a huge waste, optimized EVs tend to work the best. I have battled someone who optimizes their EVs and they are one of the toughest opponents I have ever faced.
The best way to explain it is this: The increase from 1 to 127 EVs is at least 4 times what the increase from 128 too 252 EVs is. The effect is logarithmic, and my pokemon are nearly optimized, as in the EVs are spread to the stats I think they need most but only a few are maximum. Not only do I get more of an increase from this, but the pokemon are more versatile. By sacrificing a small increase in one stat, I can put a huge increase in another.
This makes the entire team unpredictable, you could, in theory, catch opponents off guard with any member of the team. Other ways are to use moves that you never see, like soak on a Lanturn, it's very effective but rarely seen. Soak an opponent then strike them with a mega Ampharos, even those with lightning rod will go down.
Happy gaming to all, I hope you find this helpful in planning out strategies for not only Pokemon but any other PvP game.