I always knew this mon would be good. Parting Shot is a busted move and lets this Pokemon have very easy synergies with other Pokemon like setup sweepers (Kingambit, Ogerpon-W, Samurott-H, etc), and even support Pokemon like Hatterene, which appreciates the extra help to better switch into, or Lando-T. Combo of Pecha + Lando-T halves the attack of any mon, which is solid vs many Pokemon like Kingambit or Great Tusk. The supposed issue of being stonewalled by Kingambit or Ting-Lu was always cap in practice because you can easily parting on these guys and turn the table by sending whatever mon gets free setup. Malignant Chain + Tera Fairy also lets this mon cheese past a lot of Pokemon with its high defense, like Roaring Moon. If Gliscor is banned, then this Pokemon's stocks rise to the moon.
Broadly speaking, this Pokemon's statline is very similar to Garganacl, with it having a similar DoT attack in Malignant chain, but it trades the OPness of Salt Cure for Parting Shot and a better base typing.
I really like this Pokemon on Dark Spam with Pokemon like Hoopa-U, Samurott-H, and Kingambit, as this Pokemon stone walls these guy's main checks being Fighting and Fairy-types like Zama and Clefable. Samurott-H IMO is the perfect partner since Pecha can F-up almost every single remover barring Treads. It forces a 50/50 on Tusk + outspeed -> Parting Shot to lower its threat level into a more reliable check. SD Scor is also a pretty valid partner, given that its annoyed by Zamazenta.
I'm still a fan of max speed on this mon to get the clutch parting shot on Great Tusk or extra chip on Gholdengo, but max def that players are running also makes sense with how difficult Ogerpon-W can be to answer. I also think this Pokemon is one of the better Rocky Helmet users in the tier because of its insane defense, letting it make very easy progress vs many attackers or on predicted U-turns from Pokemon like Corviknight.