You’re gonna need to keep track of hitpoints and other significant statistics (from atk and def to acc and agi, and perhaps even luck if you wanna make things horribly tough and interesting). And you’re gonna have to keep track of who’s turn it is, what possible moves there are (combos, magic, minions) and how other things affect the battle (buffs, environment, damage taken). Also, I presume you’ll want some kind of leveling system to go along with it. Be sure to balance out the experience gain per fight and how much exp is required per level.
All in all, I hope you did your math homework, coz it’s formulas all the way.