How about this for size. Just tried this out on my leavanny and it definitely gets the job done competitively since she has great stats for a bug type.
Leavanny @ Focus Sash / Life Orb
Ability: Chlorophyll (If you wanna run a sun team) / Overcoat (just wait to see why!)
EV's: 4 HP / 252 Atk / 252 Spe
Jolly / Adamant Nature (I prefer Jolly for more late-game cleanup)
- Leaf Blade (Her best move. Good damage/High critical hit ratio)
- Fell Stinger / Knock Off
Okay, okay, I know but hear me out! Leaf blade... great damage helps K.O. those pesky rock and ground types, and water types get massacred (let's not talk about dual types - water/rock, water/ground, rock/ground). Then we have the almighty 30 damage fell stinger. Despite this moves super low damage it's usefulness is ridiculous... +2 attack on a 103 Atk/92 Spd Pokemon with max EV's and a chlorophyll? Literally walking on sunshine. Super sweeper. Now this is the interesting part..... Everyone knows that Leavanny gets demolished by Fire and Flying type moves. Not even Arceus can save Leavanny from a Mega-Charizard Y, butttttttt.... give her Camouflage to take away the type disadvantages during Wi-Fi play or Battle Maison play and you have yourself some pretty even playing grounds.
Camouflage gives you normal typing in those battle grounds or you could even run a terrain mon if you want a specific type. With that normal typing you get STAB Return with max happiness from just EVOLVING Swadloon to Leavanny (OMFG). Let's break it down.... 102 base damage + STAB= 153 base damage (Stronger than Giga Impact AND Hyper Beam without the turn loss) + Life Orb (extra 30% damage) = 199 base damage (quit now...) + 1 Fell Stinger revenge kill buff = GG... Just tell them to hand over their pink slips cause it's over... unless you're fighting a ghost type lol. And that's why you can choose between Fell Stinger and Knock off. Get rid of those pesky Gengars, destroy Rock/Ground/Water types. And Return everything else where it came from lol. Great set with lot's of perks. Plus you only have one weakness that people don't usually carry (Fighting). Oh and before I forget again, Overcoat ability would be great with a Camouflage Leavanny because without the grass typing you lose the powder resistances (Stun spore, Poison Powder, Sleep Powder, etc.) and Overcoat would continue to give you those benefits plus Sandstorm and Hail resistance without the Bug typing which is pretty good if you're not running a Drought/Sunny Day team/mon.
Sorry for the long explanation lol but it works.