After using it to get past the 1500s for the first time ever, I present to you
BRELOOM
I think y'all are seriously underestimating this thing. You probably know what it does on paper, at least: Spore + Stronk attacks, but I think people underestimate how seriously strong its attacks are. It finds a reasonable amount of setup opportunities due to grass/fighting's underrated resistances (dark, ground, rock, water), and once it's set up, there is NO defensive counterplay, none. Toxapex? 87.5% chance to OHKO with Loaded Dice Boolet Seed. Gliscor? 65~% chance to OHKO, and its best option is to toxic and try to protect around the attacks while you can just SD on those turns. Gholdengo? Bulldoze. Dragapult? 75% OHKO. Fully physical defensive clefable? 2HKO'd even with unaware and 4 hits, and OHKO'd at +2. Dondozo? Guaranteed 3HKO once Tera'd, loses if it switches into the wrong move. Glowking? Fully defensive set is 2HKO'd with bullet seed, not even accounting for bulldoze. Dragonite is the only thing that really walls it, as multiscale and espeed mean that it can survive rock tomb and hit back. Offense dies so hard to its mach punch too. Notably Ogerpon and offensive Ace are non-weak pokemon that are OHKO'd. It's power is really ridiculous. However, Breloom is still frail, pretty slow, and can't fit all its coverage, right? Well, yes, but I feel like people forget that it gets Spore. Picture this scenario: you've just gotten breloom in on a gliscor. Gliscor knows that breloom is really friggin scary if it sets up, so it switches to Enamorus, which Breloom can't OHKO with any unboosted attack sans Rock Tomb. If you spore that Enamorus on the turn it switches in, well, not only have you bought yourself a free turn to setup, you've removed probably the opponent's counterplay to breloom, as most teams don't pack more than 1 thing that can really defensively counter Loom. Tera also allows this to work even more effectively. Breloom SDs on the enam switchin, Teras Steel to survive moonblast, spores the enam, and now you're left with a +2 Breloom with a free turn, which I don't need to tell you is super scary. This set fits very well on Hyper Offense teams, where the slept pokemon can be exploited by another teammate even if Breloom dies. Breloom also fits very well on Veil and Webs teams, which both patch up an aspect of its weaknesses, either bulk or speed. +1 speed breloom has the ability to spam bullet seed instead of mach punch, which claims significantly more kills, and breloom behind veil often gets the opportunity to setup to +4 at which point the non-resistant checks to mach punch just... vanish.
Sorry for the long-ass post but I really wanted to get that out there. Use Breloom!