Let's go with a 500 bst. It resists fighting, ground, water, electric, and grass, while being weak to rock, flying, dragon, ice, and fairy.
HP: 70
ATK: 75
DEF: 70
SPA: 115
SPD: 70
SPE: 100
If it has access to Quiver Dance, Draco Meteor, and some good coverage, it could function as a sort of Discount Volcarona.
Here's some calcs.
+1 252 SpA Life Orb Buggon Hidden Power Ice vs. 252 HP / 24 SpD Landorus-Therian: 551-650 (144.2 - 170.1%) -- guaranteed OHKO
252 Atk Landorus-Therian Earthquake vs. 4 HP / 0 Def Buggon: 118-140 (41.8 - 49.6%) -- guaranteed 3HKO
Bulks 2 EQs from Scarf Lando.
+1 252 SpA Life Orb Buggon Hidden Power Fire vs. 0 HP / 4 SpD Magearna: 208-247 (69.1 - 82%) -- guaranteed 2HKO
This is Shift Gear Magearna, it can't do shit against AV.
+1 252 SpA Life Orb Buggon Bug Buzz vs. 0 HP / 4 SpD Tapu Lele: 231-274 (82.2 - 97.5%) -- 68.8% chance to OHKO after Stealth Rock
