While the gym leaders of Ceriah are many and varied, there are official rules that govern each gym battle. All gym battles will be single battles that utilize three Pokemon. You do not need to declare which three Pokemon you will be using and can pick them out of your six as the battle progresses. Once you send out a Pokemon it is automatically one of your three Pokemon for the match and after three of your Pokemon have been on the field you're locked into using those. The gym leader is not penalized for the challenger having less than six Pokemon and may still draw from his entire team.
The gym leader always sends his Pokemon first unless the trainer decides otherwise. Upon defeating a gym leader, the trainer is awarded credits. The first two gyms award 1,000 credits, the two after that award 2,000 credits, the two after that award 3,000 credits, and so on. Until further notice, only an admin can roleplay a gym leader. All gym battles take place within a "suppression field," a special field of energy induced around the arena that limits the levels of all Pokemon within it.
The movesets listed for a gym leader's Pokemon are only the ones most commonly used and are subject to change from match to match.