Gonna talk about a couple of sets on Pokemon I feel are a bit unexplored atm, but are really solid:
Offensive Trick Room Slowking: Trick Room as a whole is really anti-meta right now with all the HO teams flying around as TR teams turn their high Speed against them. Slowking is one of the best setters in the tier as it checks a whole host of Pokemon in RU while having Regenerator to set it up multiple times as needed. And with TR up, OTR Slowking with full coverage is really hard to switch into thanks to its bulk, "high" Speed, and coverage. Really cool set and a playstyle as a whole that I feel is pretty unexplored right now when you have powerhouses, such as MegaSnow, Druddigon, Escavalier, and Reuniclus just waiting to take advantage of the twisted dimensions.
Spikes Lead Qwilfish: This thing is horrendously underrated rn. I have sadly yet to be able to use this myself, but
aim used one against me recently and really opened my eyes to it quite a bit. Being able to always inflict serious damage on spinners and Defoggers with Explosion is really nice and Toxic Spikes is damn good atm considering one layer will really cut the lifespan of many Pokemon found on HO teams. The most common spinner in the tier, Sandslash, is grounded and lacks reliable recovery (Soft Sand variants have none at all) thus making it incredibly easy to wear down with TSpikes support.
Weather: Weather in general is something that I feel is pretty unexplored in RU, but it has really good potential, Rain in particular. There are plenty of great weather setters in the tier, such as Uxie, Mesprit, Liepard, Whimsicott, and even Meowstic-M. Whether it's rain or sun, there's plenty of Pokemon in RU that would jump at the chance to abuse it. Rain has the likes of Jolteon, Kabutops, Ludicolo, Moltres (100% accurate Hurricanes!) and Heliolisk at their disposal while Sun teams have even more with the likes of Delphox, Shiftry, Victreebel, Moltres, Emboar, and Sawsbuck. A lot of potential there, but I really feel it hasn't been explored too much as of yet.