Second favourite Pokémon overall, so I'd love to give my two cents!
Toxapex @ Black Sludge
Ability: Merciless
EVs: 4 HP / 252 Def / 252 SpD
Sassy Nature
- Baneful Bunker / Recover
- Toxic
- Venoshock
- Liquidation / Scald
The goal is to poison the enemy no matter the cost and stalling them to death with this Pokémon usually. With its Ability, it can also effectively be offensive as well! Sassy brings down its only useless stat and brings its lower Special Defence slightly higher than its Defence. Bunker and Recover serve the purpose of surviving as long as possible, one by stopping hits, the other by recovering from them. I prefer Baneful Bunker since it also lets me poison the opponent which is very important.
Toxic does what it does best: badly poisons the opponent which is preferable but not necessary. After that, it's about how to best take down your opponent. Venoshock for sure when using Poison moves since it doubles in power when the opponent is poisoned (which it will be). A must for any offensive Toxapex. I prefer Liquidation since it give a Physical option when going against Special walls, but Scald is also an option if you think Physical threats will be a problem. The IVs are to boost its best stats as much as possible while the item lets it recover between moves. Pairs up very nicely with Baneful Bunker as an annoyance.
Hope you consider this! I absolutely love Toxapex and will keep it in my team for a long time to come as well!!