How would it select "battle-winning" cards?
Short answer: use AI. 😅
Long answer: The bot should automatically learn from its own battles (and those of others) which lineups for every battle with a specific Ruleset, Mana Cap, and Allowed Splinters (and optionally, opponent preferences). 🤓 Additionally, I think that the bot should allow the player to choose which cards are best for each ruleset, mana cap, and splinters allowed. 😏