Straight writing for combat, typically it's a matter of one side posting an action (or 2 or 3) and the other side reacting and posting their own actions. Rinse and repeat, either in omegasize posts in arena forum or in a clean collab. One could make arrangements beforehand, or even throw stats/dice into an otherwise statless/diceless game, but I find not integrating those things to be preferable and find them even unnecessary if the right partners are involved.