Hmm a Poison-type Gym maybe would be fun as first Gym.

1. Gastly - 10
2. Skorupi - 11
3. Golbat - 13

Gastly because duh, most started get normal moves and can induce paralyze/sleep from Gastly's moveset
Skorupi inflicts poison, and somewhat compensates for potential bite users on Gastly
Finally a simple Golbat, not too tough, with health sapping moves.

Sort of challenge for early trainers. And before you ask me how can one get a Golbat below the level a Zubat evolves, don't ask me because there are Pokemon like that in the original games themselves.