You didn't put your team but gengar is one of the only ghost types in the early game and is pretty helpful. Mismagius is another ghost. A good dark type could be houndoom even though you get him late in game. A few other dark types are Tyranitar (Get larvitar in safari) and Umbreon makes for a great tank. Personally I would go with Gengar or Tyranitar if you have the time to train him
Umbreons pretty good if you can get it to learn dark pulse. tyranitars good too, but it has loads of weaknesses and it takes AGES to get it to evolve (level 55). i would go for gengar if you can get someone to trade with you :)
