Topped the ladder with this:
Magearna (some ball thing) @ Lum Berry
Ability: Competitive (useful for anti-Intimidate as well as the shit ton of random stat drops that happen in this meta)
Nature: Modest
Kartana (One (1) pointy boi) @ Berserk Gene
Ability: Own Tempo (I tried Defiant with a Choice Band and it works pretty well for essentially the same reasons as Competitive, but not getting screwed by two-turn moves is nice and I prefer the more immediate power. If Berserk Gene gets removed, I'll probably go back to Banded Defiant. Also note that Misty Surge does NOT work for this, because the Gene always activates before Misty Surge does even if .)
Nature: Adamant
In theory I should probably use speed reducing natures, but Magearna and Kartana both hit like wet paper towels with their "off" attack stat unless you have a ton of boosts, and both mons are common enough that speed ties are a relevant concern. Kartana does sometimes just die to a special fire or fighting move, but that's outweighed by how many times it rolls a powerful physical move and just wrecks the opponent, and it's pretty resilient on the physical side. Immunity to powder moves is nice too.