Pick a set of up to six. Bonus points for early-gen Pokemon and keeping them all the same type.
My most recent project is a ghost type team in gen 3: Dusclops, Sableye, Banette, Haunter because I couldn't trade to evolve, Shedinja before I realized how bad it actually was, and an HM mule. My pokesona would fit perfectly, being the fire/ghost regional form of Typhlosion, but sadly there's only like 2 games you can have one in so far.
Ghost type is my favorite and themed runs are so much fun!