You could create an additional Battle Arena Module that could be used by players that wish to engage in head to head combat. The arena could be another Event; take place in a stand-alone module, and have variables that tie back to game stats...Challenge Events could adapt statistic profiling in order to make things kind of even....stronger players could not deploy the number of troops that weaker players could deploy, so tactics and planning would be necessary in order to deploy the strongest troop-types against the adversaries troop-types....