Endeavor Level 1 Strats + Trick Room
Sadly starting in Generation 8 ranked battles no longer allowed the use of underleveled pokemon so therefore the Level 1 Berry Juice Endeavor Aron strategy no longer works due to the changed ruleset and it is INSANELY UNLIKELY that the ruleset reverts. However fortunately one of the confirmed pokemon, Starly is able to learn Endeavor and it being Level 1 makes it INSANELY GOOD in trick room bringing the targets down to 11 or 12 HP making it a guaranteed KO. Just give it a Focus Sash though...
Oh, and imagine that a Normal type Pokemon gets a ability that increases priority of the moves of its same type AND gets Endeavor. That would be insanely broken. Just give its partner a choice scarf to maximize the speed!
Prankster After You Quaxly
Ok, I really hope the developers accidentally make a weak pokemon into an insanely broken support pokemon like what happened to Riolu. I'm hoping Quaxly gets Prankster as the hidden ability and gets to learn the move After You as a level up/tutor/egg move. This would make Quaxly insanely overused in every single team possible. A pokemon like Choice Specs Torkoal would be an amazing partner for Quaxly. This strat would counter almost all Trick Room + Tailwind teams. The EV spreads would be Timid/Jolly 252 Speed EVs and either 252 EVs on any other stats. This strat would be countered easily by Follow Me/Rage Powder/Fake Out
Mat Block Returns
Mat Block is an insanely never-used move. This is because in Generation 8, Throh is the only pokemon that can use the move and it's transfer from Generation VII only (although his speed is terrible so Mat Block is useless anyways...) Greninja has an amazing speed stat and Mat Block would work most of the time. Hopefully a Pokemon gets to learn Mat Block and has high speed