Charles V
The play style of Charles V is a mix of the Balanced and Opportunistic AI. Unless you slip up and leave him an opening to exploit, the real race here is against the turn limit.
You start with nine gem tokens (four are gold), so your first move should be purchasing or reserving a development card. For subsequent moves, follow your preferred strategy of obtaining prestige points. To get a better score, try to impress a noble tile on your winning turn to push your point total past 20.
Mary Stuart
You have zero margin for error in this duel. Used tokens are not returned to their piles. A chess-style timer counts down from one minute, so your choices must be quick and accurate. In addition, Mary Stuart is ruthless and starts out with two points.
If you’re simply looking to win (improving your score can come later), monopolize the level 1 red development cards and go after noble tiles. When a red card is on the board, reserve it. Since the card order remains the same in every game, you can anticipate when one is about to appear.
While you’re waiting on red cards, stockpile gem tokens before Mary Stuart grabs them all. Save the gold tokens obtained from reserving development cards for important purchases.
François the 1st
The only tokens in this duel are the five gold tokens that start out in your opponent’s possession. They remain in the game no matter how many times they’re spent. The result is early round actions must be spent building your purchasing power.
Focus on three colors. Use gold tokens to make up any deficiencies when buying level 3 cards, unless there’s a development card with prestige points that will serve the same purpose. The value of the noble tiles makes them attractive targets, but they’re not enough on their own to win the game.
Like Charles V, François generally won’t win until the last round, so use that to your advantage when angling for high scores. Your highest scores come from reaching the 20 point target while impressing one of the nobles at the same time.
Isabella I of Castile
The duel with Isabella includes the highest prestige point target (25) and number of turns (33). The lack of level 2 cards and noble tiles results in games that start off slowly, but end in a rush for level 3 cards.
You’re the first to act this time, but Isabella starts off with twice as many tokens. Isabella will try to control gem tokens, so refill your stacks after she makes a purchase. Expect lean times when she’s holding a majority of gem tokens and purchasing level 1 development cards, likely out of spite. You won’t see her tokens return to the board until she makes a level 3 purchase.
Reserve level 1 development cards worth 4 prestige points when they appear, unless you have the resources to buy them outright. They’re as valuable as many level 3 development cards at a far lower cost. To close out the game, reserve and purchase whichever level 3 cards match the gems and level 1 cards you’ve been stockpiling.