Drapion is a cool one. Not only a cool design, but a great movepool too. It gained some handy moves in BW2 like Aqua Tail, Knock off, that stuff. It has a very special typing of Posion and Dark, giving resistance against Ghost, and a immunity to Psychic. However, it still has a bad weakness thanks to Poison against the Ground type, so Drapion can be very easily beaten with Eartquake or Earth Power. But we can find a way out of it.

Drapion also has some decent abilities so he can play as well offensive and defensive:
Battle Armor: Prevents Critical Hits. Acceptable. The chance of a Critical Hit at all is not as big, but its cool to prevent it. Also gives immunity to the annoying Fake Out. That is a good step to prepare if youre about to use a Swords Dance set.

Sniper: A critical hit from Drapion is not doubled, but tripled. An amazing ability. Also good in combination with Night Slash, Slash, and Cross Poison. I suggest this ability.

Keen Eye: Drapion's accuracy cannot be lowered. Although it's Drapion's DW ability, it's not really handy. There are not really much people who use accuracy-lowering moves. Double Team and Minimize are better options.

Okay, here's mah moveset:
Oops! Almost stepped in the crapion!
-Aqua Tail
-Cross Posion
-Night Slash
-Earthquake
Item: Air Balloon / Choice Band
Ability: Sniper
EVs and Nature:
Evs: 220 HP / 228 Atk / 60 Spd
Nature: Adamant (+Atk, -SpA)