What is the Simulator and what can it do?The Simulator gives you an idea of the outcome of a battle. To use the simulator, go to rally point, enter your own units and the target's units, wall level, morale, flags for the defender and/or the attacker, night bonus (if active upon command arrival), luck and affects for the defender and/or the attacker. Regarding luck, it's recommended to test what happens with -25% as the "worst case scenario".
This is relevant if you want to know whether you will win regardless of how lucky (or unlucky) you may be. Once you have set the options, the simulator calculates the outcome of the battle.