Taking the liberty of writing this for you
Theorymon, since its been a while since its been reserved and Diggersby is a rising mon that really should be covered ASAP. Feel free to credit me if you want. Not completed yet but its a good start, I'll update with teammates after more research/practice with it.
[SET]
name: Focus Sash
move 1: Earthquake
move 2: Quick Attack
move 3: Thunder Punch / Fire Punch
move 4: Rock Tomb / Swords Dance
item: Focus Sash
ability: Huge Power
nature: Adamant / Jolly
evs: 252 Atk / 4 Def / 252 Spe
[SET COMMENTS]
* Diggersby equipped with a Focus Sash serves as an effective lead and revenge killer, dealing massive damage with Huge Power boosted STAB attacks and coverage options.
* Quick Attack is used to revenge kill opposing Focus Sash or very weakened Pokemon.
* Thunder Punch allows Diggersby to revenge kill Gyarados in particular, and is also useful coverage against the likes of Togekiss and Corviknight.
* Fire Punch lets Diggersby beat a variety of Steel-types, most notably Ferrothorn and Durant.
* Rock Tomb helps Diggersby slow down Max Airstream threats such as Togekiss, and also allows Diggersby to outspeed Cinderace Sucker Punch with Quick Attack.
* Swords Dance can be opted for to boost its stats on predicted switch-outs or in order to secure a OHKO against slower Pokemon. This has the added benefit of boosting Quick Attack to help further chip incoming Pokemon.
[SET]
name: Dynamax Sweeper
move 1: Earthquake
move 2: Bounce
move 3: Thunder Punch / Fire Punch
move 4: Swords Dance / Giga Impact
item: Life Orb / Lum Berry
ability: Huge Power
nature: Jolly / Adamant
evs: 252 Atk / 4 Def / 252 Spe
[SET COMMENTS]
* Diggersby can serve as an effective Dynamax sweeper, due to its immense immediate damage output and access to Speed manipulation via Max Airstream and Max Strike.
* Bounce when Dynamaxed allows Diggersby to boost its speed through Max Airstream, outspeeding positive Speed nature Dragapult following one boost if using a maximum Speed spread.
* Fire Punch and Thunder Punch are Diggersby's way of dealing with Flying-types, in particular Corviknight, who can otherwise wall Diggersby. Fire Punch additionally allows Diggersby to OHKO Ferrothorn, while Thunder Punch allows Diggersby to OHKO Gyarados and other bulky Water-types.
* Swords Dance can be used to boost Diggersby's Attack to astronomically high levels when matched up against passive foes.
* Giga Impact can be used in place of Swords Dance to provide an immense 150 BP Max Strike, and is Diggersby's hardest hitting attack.
EV Spreads
==========
252 Atk / 4 Def / 252 Spe with a Jolly nature: Spread of choice for Life Orb sweepers, sacrificing bulk investment to hit as hard and fast as possible.
116 HP / 252 Atk / 28 Def / 4 SpD / 108 Spe with an Adamant nature: Spread of choice for Lum Berry, outspeeds up to positive natured Base 100 Speed Pokemon after a Max Airstream boost, and all unboosted Dragapult after two Max Airstreams.
[SET]
name: Choice Scarf
move 1: Earthquake
move 2: U-turn
move 3: Thunder Punch / Bounce
move 4: Body Slam / Bounce
item: Choice Scarf
ability: Huge Power
nature: Jolly
evs: 252 Atk / 4 Def / 252 Spe
* Diggersby with a Choice Scarf allows Diggersby to outspeed unboosted Dragapult without any boosts, helping it serve as a potent revenge killer and scout.
* U-turn lets Diggersby break Focus Sash and Disguise, while also allowing Diggersby to switch to more favorable matchups.
* Thunder Punch helps Diggersby beat Flying-types, like Gyarados and Togekiss.
* Bounce can be used to stall out Dynamax turns, and also has the added bonus of boosting speed while using Max Airstream. After Dynamax concludes, Diggersby becomes faster than most Choice Scarf users at +1 Speed.
* Body Slam is an alternative STAB choice, dealing heavy damage at neutral.
