Jirachi @ Leftovers
Ability: Serene Grace
EVs: 252 HP / 224 Def / 32 Spe
Impish Nature
- U-turn
- Iron Head
- Thunder Wave
- Healing Wish
Let's face the facts of today's meta, Diggersby's 85 / 77 / 77 defensive stats combined with a lacking speed stat limit it's uses for wall breaking. Diggersby needs support, it's practically begging for slow VoltTurn 'mons and Healing Wish. Jirachi is a shoe in candidate, providing Diggersby with free switch-ins, speed control in T-Wave and a second chance to sweep late game. The build is
stolen adapted from the standard SpD set, favoring Def EVs to survive AoA Weavile's Knock Off. Even without any SpD EVs, Jirachi is still competent in handling special attackers it's meant to check, like LO Latios.
252 Atk Life Orb Weavile Knock Off (97.5 BP) vs. 252 HP / 224+ Def Jirachi: 289-343 (71.5 - 84.9%) -- guaranteed 2HKO after Leftovers recovery
252 SpA Life Orb Latios Draco Meteor vs. 252 HP / 0 SpD Jirachi: 138-164 (34.1 - 40.5%) -- 44% chance to 3HKO after Leftovers recovery
252 SpA Life Orb Latios Hidden Power Fire vs. 252 HP / 0 SpD Jirachi: 172-203 (42.5 - 50.2%) -- guaranteed 3HKO after Leftovers recovery
With the 32 Spe EVs, Jirachi outspeeds notable switch-ins of Adamant Bisharp, non-scarfed TTar, and standard SpD Heatran, all of which are obliterated after a U-turn to Diggersby. Weavile's typing presents a huge threat to this partnership, but with a T-Wave and a Healing Wish, our Diggsy can stomach the Ice Shard and OHKO Weavile.
Just some other options: Jirachi can provide rocks with the U-turn chip damage to aid Diggersby's role in wallbreaking, however it's difficult to give up one of its more valuable moves. Jirachi can also make use of Trick Room, patching up Diggs lack of speed and allowing it to take on faster, offensive threats. Diggersby with a -Spe nature and 0 IVs and EVs lets it move before neutral nature base 60 'mons and allocate those EVs to max out its HP stat.