Well, you're at least familiar with HeroScape, so you know of one combat system. Roll dice equal to attack, each with some chance of some success, roll dice equal to defense, each with some chance of some success, inflict the difference in damage. You compare your game with HeroScape; what will be different about your game? What do you want to keep the same? Are you having basic attack/defense style stats, or something more out of the ordinary? It's tough to just attach a mechanic to nothingness, otherwise you get uber-basic possibly-sarcastic responses like Mr. Man Lan's.