Sableye-Mega @ Sablenite
Ability: Prankster
EVs: 248 HP / 252 Def / 8 SpD
Impish Nature
- Protect
- Foul Play
- Toxic
- Recover
So Pex is considered the only halfway decent Toxic Spikes user in the tier (with Gren, Cloyster, and Tentacruel maybe being able to set up on HO teams). Pex has many coveted traits, including high base defenses (50/152/142), great defensive typing (including important resistances to Fairy, Water, Ice, Fire, Steel, and Fighting), good defensive movepool (including Haze, Infestation, Recover, and the aforementioned Toxic Spikes), and the best non-broken ability in Pokémon (Regenerator; Moody for best broken ability).
Mega-Sableye is an under-utilized defensive Pokémon in the AG metagame, being able to single-handedly shut down numerous offensive and defensive threats. Offensive Pokémon checked include Marsh, DeoA, MMX, non-Choice Band Mega-Ray, non-Z SD Arc (Ekiller is entirely countered), and SD Ultra-Necro. Defensive Pokémon include defensive Mewtwo, non-set up Zygarde, Lugia, Gira, defensive Ho-Oh, Ferro, Celes, Skarm non-Z SpDef DM, Tyranitar, Chansey, Blissey, Goth, Mega-Sableye, and Arc-Poison (kinda). Suicide leads, like Shuckle, Deoxys-Speed, Smeargle (kinda), and Aero (Arc-Fairy and Exca withstanding), are stopped in their tracks. This slows down the game to MSab's preferred defensive style. Seriously, Mega-Sableye is so good.
Pex switches into Fairy-type attacks for Mega-Sableye and Sableye can counter the Psychic-type attacks for Pex. Sableye can Fake Out/Protect to rack up poison damage, meaning Pex is suddenly becoming a looming defensive endgame.