I've been playing around for a bit ever since I knew of the existence of this glorious little pin cushion that I have undying love for, and I think I've gotten a pretty nice set/spread going with it.
Toxapex @ Black Sludge
Ability: Regenerator
EVs: 248 HP / 148 Def / 112 SpD
Calm Nature
IVs: 0 Atk
- Recover
- Scald
- Toxic
- Haze/Infestation/Toxic Spikes
So, the moves.
Recover is very self-explainatory for this self-sustaining wall of a pokemon. Giving it active healing whenever it so desires.
I juggled between Scald, Poison Jab, and Venoshock, but ultimately, I ended up at Scald. It's the best offense this thing has, to be perfectly honest. It gives it some amount of offensive pressure, it hurts Steels and Poisons, and it can cripple physically terrifying opponents. Of course, it does go against the poisoning a bit, but overall, it's usually better than poison STABs it's got. You can also use Liquidation, if you're bothered by the random burns.
Toxic allows Toxapex to do what it does best, stall. It whittles down opponents while adding pressure.
Now the 4th move slot was a bit tricky. I played around with Stockpile first, but this mon doesn't have the pressure to stop the opponent from setting up in your face. Haze overall is a good stop to win-cons and set-up sweepers while also setting the scene for another pokemon to finish up the opponent if it has a sub up or an unfavorable typing against Toxapex. Infestation is... a favorite of mine. I've used a lot of cancer Dusclops in NU with Infestation with many more mons with Infestation, and for this pokemon, Infestation just fits the bill quite well. If the opponent has no switch-in to a poke that has active recovery, set-up (which you could argue that you could run Haze along with this), or something to 2-shot this thing, they're almost good as gone, 9/10 times. Toxic Spikes is another good option for it, dealing some nice procedual damage to the party just after one turn.
Now, Haze is quite essential, and you can run it over say, Scald for ultimate stall, but then its use really narrows from a wall to a staller.
The spread.
There's a lot of threats for Toxapex: Scarfed Xurkitree, Banded Dugtrio, Landorus-T, DD Kommo-o, Tapu Lele, Magnezone, M-Metagross...
This spread basically allows it to potentially live all of the attacks these things can throw at it. Let's go over the calcs.
252 SpA Xurkitree Thunderbolt vs. 248 HP / 112+ SpD Toxapex: 228-270 (75.2 - 89.1%) -- guaranteed 2HKO
It can tank a TBolt from a Xurkitree and possibly another after Sludge recovery and regenerator, though they usually use Volt Switch instead.
252 Atk Choice Band Dugtrio Earthquake vs. 248 HP / 148 Def Toxapex: 254-302 (83.8 - 99.6%) -- guaranteed 2HKO
The Def EVs given to it allows it to barely hold on after a banded EQ from arguably one of the best trappers of the current meta and proceed to usually kill it afterwards.
252 Atk Landorus-Therian Earthquake vs. 248 HP / 148+ Def Toxapex: 204-240 (67.3 - 79.2%) -- guaranteed 2HKO
Landorus-Therian doesn't even come close to knocking out this pin cushion.
+1 252+ Atk Kommo-o Earthquake vs. 248 HP / 148 Def Toxapex: 200-236 (66 - 77.8%) -- guaranteed 2HKO
Now, I'm not exactly sure if Kommo-o uses EQ or runs Adamant, but even if did, this is the best it could do against Toxapex, and then it just proceeds to kill all of its stat boosts and Regenerator switches afterwards.
252+ SpA Choice Specs Magnezone Thunderbolt vs. 248 HP / 112+ SpD Toxapex: 300-354 (99 - 116.8%) -- 87.5% chance to OHKO
252+ SpA Magnezone Thunderbolt vs. 248 HP / 112+ SpD Toxapex: 200-236 (66 - 77.8%) -- guaranteed 2HKO
Only a Specs Magnezone can outright OHKO Toxapex, and I think that Magnezone is somewhat obselete because of Xurkitree nowadays.
252 Atk Tough Claws Metagross-Mega Zen Headbutt vs. 248 HP / 148+ Def Toxapex: 212-252 (69.9 - 83.1%) -- guaranteed 2HKO
Even the all-powerful Mega-Metagross can only dream of killing Toxapex.
252 SpA Tapu Lele Psychic vs. 248 HP / 112 SpD Toxapex: 300-354 (99 - 116.8%) -- 87.5% chance to OHKO
Maybe the best killer for this set is Tapu Lele in Psychic Terrain, since it can very safely dispose of Toxapex 7/8 times.
And just for fun...
252 SpA Choice Specs Jolteon Thunderbolt vs. 248 HP / 112 SpD Toxapex: 266-314 (87.7 - 103.6%) -- 18.8% chance to OHKO
Even Specs Jolteon very uncommonly straight up OHKOs Toxapex.
So, to sum it up, in my opinion, this spread allows Toxapex to harness its potential to the fullest while being the most toxic of thorns in the opponents back.