Card battle can take many directions.
Most people are familiar with the rules for Magic The Gathering; but there are also many many other game formats as well!
In Colossal Arena, for instance, you are a wealthy aristocrat who bets on the outcomes of which monster will win the arena battle. All sorts of sneaky tricks are pulled to make your gambled money worth it. Link here: https://boardgamegeek.com/boardgame/105/colossal-arena The role of the player changes the feel of the game.
I would highly recommend taking a look at many other games on Boardgame Geek and seeing what mechanics they have there.