Nihilego

Poison

Nihilego is a powerful revenge killer and sweeper available to Poison teams thanks to its solid Speed, expansive movepool, and solid Special Attack. Nihilego's already high Special Attack stat can be amplified to greater levels thanks to Beast Boost, as it becomes harder to stop with each KO it gets. Its unique speed tier allows it to outspeed and KO foes such as Garchomp, Landorus, and Victini. Nihilego's ability to use Stealth Rock is critical for chipping away at opposing pokemon, as it can reliably pick up extra KOs and gain more boost from Beast Boost as a result. It also compresses the role of a Stealth Rock setter well, as it can force many powerful threats such as Kyurem-B out. However, Nihilego's terrible defensive typing makes it susceptible to Ground-, Psychic-, Steel-, and Water-types such as Hippowdon, Mega Gallade, Jirachi, and Mega Swampert. Its Rock- and Poison-type STAB move combination also is rather poor against a majority of foes, including Heatran, Jirachi, and Gastrodon. Nihilego also must constantly run coverage moves such as Hidden Power Ice and Thunderbolt in order to check foes such as Gliscor and Toxapex. Additionally, while it has very good special bulk, Nihilego's horrendous physical bulk leaves it susceptible to many physical attackers and priority users such as Azumarill, Bisharp, Breloom, and Scizor.

Rock

With its powerful offenses, diverse coverage options, and unique defensive utility, Nihilego is one of Rock's strongest special attackers. Access to valuable coverage moves like Thunderbolt and Grass Knot allows Nihilego to put heavy pressure on the Water and Ground teams that Rock can struggle with. Thanks to these coverage moves and its good Speed tier, Nihilego can outrun and check key threats such as Garchomp and Landorus. Nihilego's Speed tier also lets it clean through weakened teams in conjunction with Beast Boost. Furthermore, its Poison typing offers valuable neutralities to Fighting- and Grass-type moves, which Rock is weak to, as well as a means of removing Toxic Spikes, and its high Special Defense lets it serve as a check for special attackers such as Alolan Raichu and Greninja, especially with sand support. However, Nihilego's middling Defense leaves it vulnerable to many physical attackers such as Mega Lopunny and many common priority users such as Azumarill and Scizor, and despite its good Speed, Nihilego is still outsped by key threats such as Terrakion and Keldeo that threaten Rock as a whole. While Nihilego has a deep movepool, it is not able to cover everything with four moveslots and will always have a gap in its coverage opponents can exploit.