Dreepy doesn't have a great movepool. That's a fact. But its stats are reasonable for an LC competitor, (a little lopsided but the point stands). So, here's the best set I could muster from Dreepy's limited movepool:
[email protected] Scarf/Black Glasses
EVs: 252 Atk, 252 Spd, 4 HP
Not the best. I know. Anyway, let's start by explaining the item. This Dreepy is running exclusively normal and dark moves, so an item the buffs one of them would be nice (Facade and Sucker Punch are stronger, so you might want the Silk Scarf to buff the weaker Quick Attack or the Black Glasses to buff Bite) Inflitrator is there to get through various screens and subs. The EVs are standard physical sweeping EVs (the HP is a little redundant but you never know). Adamant and Jolly natures buff attack and speed, respectively, and lower special attack, which you won't be using at all. As for the moves, Sucker Punch and Quick Attack are priority, Bite can flinch, and Facade is better than the rest of Dreepy's attacking moves (Infestation, Dragon Tail, Astonish, Snore, Swift and Round).