I’m drawing inspiration from a couple different places – It’s a mix of sport fencing, rock paper scissors, magic the gathering, and street-fighter, with 4e’s powers template for organization and balance.
Essentially, every character will have a pool of actions, derived from race, class, and background, as well as default actions that everyone has access to at all times. These are assembled into a deck, and a player builds a hand of several cards. Each action has a force rating, determined by whether it’s a powerful attack, or a quick one, or a sneaky one, etc.
When an adversary is engaged, someone plays an attack card – by beating the force rating of the preceding card, the defender can try to counterattack – this alternates back and forth until a character cannot beat the force rating, or chooses not to – at which point damage is applied. If force ratings are tied, both participants suffer damage. At that point, all played cards are exhausted.
At the end each combat round, a limited number of actions are randomly refreshed for every adversary.