Moves
Shadow Ball is Blacephalon's most spammable STAB attack and is great in many matchups, such as against Psychic teams. Fire Blast is Blacephalon's chosen Fire-type STAB move, enabling it to deal considerable damage in the sun, even against resisted targets, always 2HKOing Hydreigon for instance. Flamethrower is an alternative if Fire Blast's accuracy is an issue, but its lowered damage output makes Blacephalon miss out on OHKOing threats like Tapu Koko and 2HKOing others like specially defensive Cradily in the sun. Hidden Power Ice lets Blacephalon KO troublesome Dragon- and Ground-types like Dragonite after its Multiscale is broken, Garchomp, and Choice Scarf Landorus-T. Psyshock allows Blacephalon to revenge kill Choice Scarf Nihilego, one of the greatest threats for Fire teams, and take on Poison teams once Alolan Muk is eliminated. If crippling walls is desirable to your team, Trick can be used instead to shut down foes like Chansey and Mantine that Blacephalon cannot otherwise touch.
Set Details
Maximum investment in Speed with a Timid nature and a Choice Scarf lets Blacephalon be as fast as possible, outspeeding opposing Choice Scarf users like Nihilego and Victini. It also needs maximum investment in Special Attack to hit as hard as possible. With those EV investments, Blacephalon's ability Beast Boost will boost its Special Attack by one stage every time it KOes an opposing Pokemon, enabling it to clean weakened teams late-game.
Usage Tips
Send Blacephalon on the field after its checks, such as Chansey and Toxapex, are weakened or gone, so that it can effectively sweep the enemy team. However, because Blacephalon is extremely frail, directly sending it onto the field is not recommended. Instead, use a teammate's slow U-turn or Volt Switch or switch in Blacephalon after a teammate has been KOed to preserve its health. For Blacephalon to efficiently sweep teams, it will more often than not need Stealth Rock support from a teammate before it's able to revenge kill fast or bulky offensive threats like Tapu Koko and Dragonite. Therefore, setting up the entry hazard before sending Blacephalon onto the field can be crucial. Pursuit users like Tyranitar and Alolan Muk threaten to KO Blacephalon and take minimal damage from its coverage moves. Therefore, it would be best to either avoid bringing Blacephalon onto the field while they're healthy or to immediately switch Blacephalon out as a lure into an offensive teammate that can handle them. Furthermore, if an opposing Pursuit trapper is alive, revenge killing dangerous threats like Choice Scarf Nihilego can be problematic, as they simply switch on Blacephalon and easily KO it. So, if possible, try and dispose of such threats with one of Blacephalon's teammates that wouldn't be bothered as much by Pursuit trappers. If Trick is run over Psyshock, it can be used to great effect by luring and crippling problematic walls like Chansey, Mantine, and Toxapex that Blacephalon cannot seriously harm otherwise so that they become deadweight for the rest of the match. Finally, try and avoid any kind of status, especially paralysis. A paralyzed Blacephalon cannot efficiently perform its role as a revenge killer due to its greatly reduced Speed stat and becomes a lot easier to revenge kill, being outsped and OHKOed by Mamoswine's Earthquake for example.
Team Options
Choice Band Infernape is an amazing partner for this Blacephalon variant: it can punch holes in the enemy team so that it's easier for Blacephalon to sweep, safely bring it on the field with U-turn, and beat troublesome Dark, Rock and Normal teams with Close Combat and Iron Fist-boosted Mach Punch. In return, Blacephalon can sweep Psychic and Ghost teams, which Infernape has trouble with, with little support. Mega Charizard X forms a potent sweeping duo with Blacephalon that can beat each other's checks and tear opposing teams apart. For example, against Poison teams, Mega Charizard X takes care of Alolan Muk for Blacephalon, which paves the way for Blacephalon to sweep the rest of the Poison team with Psyshock. The support Torkoal brings to Blacephalon and Fire teams in general as a sun and entry hazard setter, spinner, and physical wall is really important, since it can enable Blacephalon to OHKO Zapdos after Stealth Rock damage and Mega Lopunny in the sun while clearing entry hazards away and easily sponging most priority moves aimed at Blacephalon. Rotom-H is a nice teammate for Blacephalon due to its access to a slow Volt Switch, both Light Screen and Reflect, and Defog, which lets Blacephalon safely come onto the field, clean opposing teams more easily, and not worry about entry hazard damage or opposing screens cutting its sweep short. Rotom-H also brings a welcomed immunity to Ground-type moves for Fire teams. In return, Blacephalon can KO many Ground-types like Landorus and Garchomp, which Rotom-H ironically cannot touch, with Hidden Power Ice. Mega Charizard Y is an appreciated secondary weather setter and wallbreaker that pressures opposing Water-types, easing Blacephalon's job of cleaning the enemy team late-game. Victini is another wallbreaker that pressures Water-types, especially Mantine, so that Blacephalon has more opportunities to clean the opposing team. Furthermore, it can even safely bring Blacephalon onto the field with U-turn. Heatran can trap and remove bulky threats like Toxapex, letting Blacephalon have an easier time sweeping the enemy team, and can KO Mega Diancie with Flash Cannon. Volcanion can act as a check to troublesome Water-types with Water Absorb, such as Azumarill, and a secondary hazard clearer with Defog for Blacephalon.