Clawitzer4 should also OHKO Slowbro with Dark Pulse. What's the reasoning for the 148 HP / 108 Def / 252 SDef EV spread? Running 148 EVs in HP instead of 252 on Slowbro doesn't seem optimal.Well, I gots a decision to make, a decision which requires more breeding, but could pay off in the end.
Having cleared another 48 battles (bringing Aron to 108), I decided to compile a list of things that can prevent a first-turn TR by offing Slowbro:
148/108/252+ Sassy Slowbro checks:
Choiced: Porygon-Z 2, Slaking3, Tyrantrum4, Archeops3, Armaldo4, Thundurus2, Haxorus3 (requires Rivalry, female)
Megahorn: Escavalier 1,3,4, Heracross 3,4
Solarbeam: Vileplume2, Tangrowth3, Victreebel4, Vileplume4 (must lead with Drought Ninetales or follow enemy Sunny Day)
Leaf Storm: Victreebel2, Roserade3, Exeggutor3, Serperior4
Guess: Landorus1, Articuno2, Tyrantrum3, Bastiodon3, Mamoswine3, Vanilluxe3, Cryogonal3, Pinsir4, Whiscash4, Wailord4, Walrein4, Donphan4
Now, by switching the nature to Bold, it takes the Tyrantrum4 and Heracross OHKOs off the table, meaning under the circumstances we've come to expect by leading with Aron, the AI will not target Slowbro with their respective strongest moves.
The only OHKO I noticed it immediately added was Ampharos4, giving its Thunder a 50% chance to do the job, and I can confirm that the possibility of a OHKO, even a 25% chance, is enough that the AI will go for it. I used Magnzeone4 as a barometer of what can and can't do the job (Thunderbolt from Modest 252+ does 98% max) with Chandelure and Volcarona to test their best SE STAB move of their types also. Surprisingly, Latios3 with its Specs Draco Meteor still doesn't come as close as those three could.
Escavalier is still bad news, having just enough attack over Heracross to keep the odds for a OHKO.
The main thing making me hesitate is the fact that I've fought a *lot* of Ampharos4 up to this point, and with my current spread, that 50% is higher odds than most unguaranteed OHKOs aside from the choice users (87% chance for Thundurus with the Sassy build) and it also turns the Thundurus and Vileplume into guaranteed OHKOs. Neither of those two pokemon are particularly rare, and while Vileplume relies on sunlight to be in effect by the time it attacks, it's gotta happen at some point, right?
So, while the Bold nature takes two Set4 OHKOs away, it also ensures Slowbro'll always be killed by at least two more should they target it, plus adds Amphy to the group of threats. As it stands, the odds of Heracross4 and Tyrantrum4 getting a OHKO on Sassybro are not very good (25% and 31% respectively) but hell, I was critted by a fucking male Rivalry Haxorus, so that doesn't really mean shit, does it.
Opinions, anyone?
I'm not a fan of Slowbro as a setter in general for the reasons you state - with the Dark/Ghost/Bug weaknesses of Psychic and an Electric/Grass weakness from its Water-typing, it has a lot of weaknesses to common-ish strong attacks - way more than you'd like on a TR setter. A type resist berry could alleviate one of its weaknesses (maybe a Bug-resist berry with Sassy to cut out Armaldo, Escavalier and Heracross?), but that's an expensive item and only alleviates a few threats.