Magnemite When you're writing this, make sure to mention that SD Diggersby in particular requires Stealth Rock / general entry hazard support, since some OHKOes aren't guaranteed without them:
- +2 Quick Attack vs. 4 HP / 0 Def Latios: 265-313 (87.7 - 103.6%) -- guaranteed OHKO after Stealth Rock
- +2 Quick Attack vs. 4 HP / 0 Def Mega Charizard X: 200-238 (67.1 - 79.8%) -- 37.5% chance to OHKO after Stealth Rock
- +2 Quick Attack vs. 4 HP / 0 Def Pinsir: 187-222 (68.7 - 81.6%) -- 50% chance to OHKO after Stealth Rock (if it switches in as normal Pinsir)
- +2 Quick Attack vs. 4 HP / 0 Def Latias: 242-285 (80.1 - 94.3%) -- 43.8% chance to OHKO after Stealth Rock
- +2 Quick Attack vs. 4 HP / 0 Def Landorus: 242-285 (75.6 - 89%) -- 12.5% chance to OHKO after Stealth Rock
- +1 Return vs. 252 HP / 252+ Def Landorus-T: 324-382 (84.8 - 100%) -- 81.3% chance to OHKO after Stealth Rock (after Intimidate)
- +2 Quick Attack vs. 252 HP / 0 Def Azumarill: 265-313 (65.5 - 77.4%) -- 25% chance to OHKO after Stealth Rock and 1 layer of Spikes
- +2 Return vs. 252 HP / 252+ Def Hippowdon: 360-425 (85.7 - 101.1%) -- 50% chance to OHKO after Stealth Rock (yeah I know nobody really runs phys def Hippowdown, it's good to be prepared, and the fact that you can OHKO the mixed defensive variant without even trying is cool in itself)
And yeah overall, you get my point, it's auxiliary, just like on any offensive Pokemon, and these Pokemon are stuff you're likely to see these days. Just mention Pokemon than can perform quick!spikes or quick!SR and you should be dandy.