Ok, first thing: challenge Dr.Dynamite, Chingstah, or myself to tryout for a gym.
Gyms teams are Mono-Type and allowed up to two Pokemon that are of totally different types (Also known as Wild Cards).
For example, you can have a Fire Gym with 4 fire types, and 2 water type Pokemon for strategy, coverage, defense, etc.
All teams are OU. If a Gym would like to have Double battles or Triple battles, they are allowed, but you must specify along with any other rules.