Moves
Giga Impact is Diggersby's go-to STAB option, able to one-shot threats like Kommo-o, Mega Altaria, Meloetta and Primarina. Earthquake hits Pokemon like Zeraora, Mega Metagross, and Magearna. Superpower is run in order to KO Heatran, Type: Null, and Umbreon. Fire Punch can be run in order to OHKO Mega Scizor and physically defensive Ferrothorn. Ice Punch is an option to beat Occa Berry Whimsicott and non-maximum Defense Zygarde-C and fish for potential freezes in unwinnable matchups. Foul Play can be run in order to lure in and OHKO Magnet Rise Mega Metagross.
Set Details
120 HP and 4 Special Defense EVs are run in order to always survive an Ice Punch from Mega Metagross and an Overheat from Heatran and to give Choice Scarf Genesect an Attack boost instead of Special Attack from Download. 196 Speed EVs enable Diggersby to always outspeed Magnezone, which could potentially 2HKO with Flash Cannon, as well as neutral-natured Volcanion and uninvested base 100 Speed Pokemon like Manaphy. 188 Attack EVs are run in order to maximize Diggersby's Attack as much as possible, granting it absurd matchups against some of the physically bulkiest Pokemon in the metagame, like Mega Altaria, Primarina, and Meloetta. Huge Power is run in order to double Diggersby's Attack, aided by Choice Band as well.
Alternatively, a simple 252 Atk / 4 SpD / 252 Spe set with an Adamant nature allows Diggersby to OHKO Waterium Z Tapu Fini and outspeed and OHKO niche threats like neutral-natured speedy Tapu Bulu.
Usage Tips
If one of Diggersby's coverage moves can OHKO the foe, use it over Giga Impact, as this will circumvent any chance of losing due to a miss. It is relevant to know that Choice Band Diggersby, as one of the most physically powerful attackers in 1v1, can win against foes that would normally be able to tank a neutral or even super effective hit from almost anything else, including bulky Mega Charizard X, Meloetta, Kommo-o, Primarina, Tapu Fini, Mega Altaria, Clefable, maximum Defense Hoopa-U, and almost always Mega Swampert. Physically defensive Tapunium Z Tapu Fini is not consistently OHKOed by Giga Impact, so instead use Earthquake to 2HKO.
Team Options
Diggersby is deathly weak to basically any faster offensive threat, like Dragonite, Mega Gyarados, Mega Charizard X and Y, Greninja, and Porygon-Z, as well as Pokemon like Smeargle and Jumpluff, whose strategies rely on putting an opponent to sleep first, then stalling with Leech Seed. Therefore, stall users that can set up against their defenses and mitigate sleep strategies, like Type: Null, Mega Slowbro, Mega Sableye, Mega Audino, and Deoxys-S, act as reasonable support for Diggersby. They in return appreciate Diggersby's ability to annihilate common Taunt attackers, like Kommo-o, Mega Mawile, and Tapu Fini, as well as Pokemon like Incineroar, Meloetta, and Aegislash, which all have strategies that can ignore stat boosts. Outside of Magnezone, Sturdy Pokemon like Donphan, Golem, and Carracosta will threaten Diggersby, as it will be unable to break them fast enough due to their innate ability. To threaten these Pokemon, bulky Water-types like Mega Gyarados, Primarina, and Tapu Fini can be run, alongside some other faster threats like Mega Charizard X and Y, Greninja, Dragonite, and Mega Lopunny. In return, they appreciate Diggersby's positive matchup against Electric- and Grass-types like Zeraora, Magnezone, Ferrothorn, and bulky Tapu Bulu, as well as opposing Primarina and Tapu Fini, and certain bulky Pokemon like Meloetta and defensive Hoopa-U.