Komala (M) @ Leftovers
EVs: 8 HP/ 250 Def/ 250 Sp. Def
Nature: Impish (+Def, -Sp. Atk)
• Play Rough
• Substitute/Bulk Up
Return: If you max out happiness, Return would have 102 base power + STAB = 153 base power.
Play Rough: Use it for Ghost and Rock and for super effective damage.
Wish: Self-explanatory; just tick off your opponents one by one.
Substitute/Bulk Up: Komala isn't the bulkiest Pokemon, so these are good moves to boost defense (for the latter, anyway). However, if you can use Substitute and Wish properly, go with that.