Breloom has proven to be just as amazing, if not, even better in this gen of pokebilities compared to prior gens for multiple reasons such as terastalization and Loaded Dice. However, there are two specific pokemon that often infinitely switch in on Breloom if they're careful about hazard removal, those two being Azumarill and Farigaraf. I originally tried making a Roseli Berry set for Breloom with Gunk Shot, but I ended up finding that I'd often still get OHKOd by banded Play Rough even through Roseli Berry, Gunk Shot just wasn't enough to KO Azumarill often, and I wasn't staying in on Azumarill enough anyway to make Roseli Berry be worthwhile. After that, I did calcs with Expert Belt and realized it 2HKOd Farigiraf even without a super effective boost and min roll Gunk Shot into Mach Punch kills 252 HP 4 Def Azumarill, so Belt didn't help much. The best items on this set will probably end up being the items that Breloom already runs such as Loaded Dice, Toxic Orb, Focus Sash, and Choice Band.
TL;DR, do your calcs before trying to come up with cool sets to beat one single pokemon so you don't waste multiple games testing something completely suboptimal
TL;DR, do your calcs before trying to come up with cool sets to beat one single pokemon so you don't waste multiple games testing something completely suboptimal