RPG Engine Help

[i8bit]

First off, allow me to explain what I'm trying to do. I'm sure everyone has played one of the original Final Fantasy, or even Pokemon games. You're roaming around, and then BOOM, you encounter an enemy and you are in battle.

My battle system is complete, but I'm having trouble grasping my mind around how to get the player to change to his/her own private level to fight that specific enemy. If a player is in battle, I don't want other players to join that same battle.

Any thoughts?