Battles between players and monsters are considered to be the core issues of RPG games, and they are something that effects the players the most when it comes to thinking whether that particular game is fun or not. Even though MMORPGs have enabled RPGs to get out of the repetitiveness into unlimited possibility of expandability and capability of modification of game plays, essential game play process remains still important - the basic battle between the player and the monsters. In this research, we made a simulator to simulate the process of the battles to estimate results of battles by pre-testing the battles with setting up the experience values of players and monsters using formulae needed for the battle systems at the beginning of game development. It can be utilized at a tester to find out a better configuration of monsters in the maps for better optimization of time and efficiency of the battles to satisfy the game planning.