hi
Overview
########
Diglett reaches 20 Speed, making it the fastest unboosted Pokemon in the metagame alongside Elekid and Voltorb. It has a fantastic ability in Arena Trap, allowing it to trap and remove specific threats. This is particularly good for Pokemon like Fletchling who need Chinchou gone. Despite these two great qualities, it is weak without a Life Orb and it's incredibly frail without Focus Sash which makes it difficult to switch into anything.
Trapper
########
name: Trapper
move 1: Earthquake
move 2: Rock Slide / Thief
move 3: Substitute / Protect / Stealth Rock
move 4: Sucker Punch / Memento
ability: Arena Trap
item: Life Orb / Focus Sash
evs: 36 HP / 236 Atk / 236 Spe
nature: Jolly
Moves
========
Earthquake is Diglett's main STAB attack, KOing most weakened Pokemon and is the only staple Diglett needs in its otherwise customizable move set. Rock Slide is Diglett's primary coverage move, hitting Fletchling, Vullaby and other Flying-types. Substitute lets Diglett bypass Sucker Punch, which is particularly useful for trapping Pawniard, and also allows it to avoid status. Protect can be used to avoid Fake Out. Memento is a good last ditch effort after Diglett revenge kills an opponent to avoid the opposing Pokemon setting up and giving your own Pokemon a chance to set up. Thief is also an interesting option with Focus Sash, because it allows Diglett to get rid of an opponents item before it faints which may be more important than a Memento, especially early in the game on a Pokemon like Mienfoo. Shadow Claw can also be used over Thief with Life Orb, since Diglett will generally be keeping its item. Sucker Punch lets Diglett KO Pokemon that use priority such as Fletchling. Shadow Claw can also be used here for a more reliable way to hit Misdreavus. Diglett can also use its Speed to set up Stealth Rock before it is KOed if nothing can take advantage of Memento and Sucker Punch is not needed.
Set Details
========
The EVs maximize Speed and Attack with the leftovers put into HP. Life Orb gives more immediate power and does not limit its usefulness later in the game with hazards up. Focus Sash lets Diglett more reliably switch into Pokemon such as Chinchou if hazards are not up. It also is the only reliable way to get rid of Choice Scarf Pawniard.
Usage Tips
========
Diglett is not bulky enough to be switched into many attacks, even weak ones, so it is best to keep it for revenge killing unless there's a predicted Electric-type attack or a slow U-turn, Volt Switch, or Baton Pass. If Focus Sash is used, it's best to use a Defogger even if Scarf Pawniard switches in since it can always take the hit and return a KO regardless of being +2. Diglett can technically trap anything that is not immune to Ground-type attacks, but its most reliable at removing Pokemon it can KO, such as Magnemite or Trubbish. Diglett is fairly weak, so it's important to make sure your opponent cannot set up after Diglett KOes something.
Team Options
========
Diglett is best paired with something that benefits from the trapping of Chinchou or other Electric-types such as Magnemite. This includes Pokemon such as Fletchling and Taillow. It also traps Poison-types, which Spritzee needs removed along with Steel-types, making it a great teammate. It also benefits greatly from slow U-turn users or hazards of its own to break Magnemite's Sturdy or weaken the opponent to Diglett's KO range. Knock Off support is very useful for bringing more things into Diglett's KO range.
Other Options
#########
Diglett can also run a Choice Scarf set to revenge kill other Choice Scarfers such as Pawniard or weakened set up sweepers such as Scraggy. It can also run Berry Juice along with Substitute and Thief as a cool way to remove an opponent's item.
Counters
#########
**Flying-types/Levitate**: These Pokemon will not take much damage from any of Diglett's coverage moves even if they are super effective. They can also switch out from Diglett's Arena Trap.
**Physically Bulky Pokemon**: Diglett is not very strong, so Pokemon such as Mienfoo, Spritzee, and Slowpoke, while not immune or resistant to Earthquake, will still not be easily KOed by it and can deal heavy damage in return.
**Priority**: Due to Diglett's incredibly weak defenses, most priority moves will OHKO it meaning it is easily revenged.