So mechanics question. Does the cost of the card you set aside have to be 4 the first time you play Prince, or does its cost have to be 4 or less at the end of each turn from then on out? The wording seems to imply that it only has to cost 4 when you initially play Prince and set the card aside with it. This seems crazy strong.
Also, if you Prince the King's Court, and play a duration card with it, would the King's Court get set back on the Prince, or would it go with the duration card, thereby losing it's Prince status afterward?
It only has to cost $4 when you play Prince, and a Prince'd Throne will lose its magic if you use it on a duration card.
Prince FAQ
Prince has you play the same cheap action every turn for the rest of the game. The turn you play Prince, you set it aside with an Action from your hand costing $4 or less; then every turn after that you play the Action at the start of the turn, and then set it aside again when you discard it from play. If you don't discard the Action then you stop playing it with Prince; Prince at that point is just set aside doing nothing for the rest of the game. That won't normally happen but will happen for example if the Action is a Feast or Mining Village and you trashed it, or if it's a duration card and so it stayed in play, or if it's a Madman and was returned to its pile, or if it's an Island and was set aside, or if it's a card you put back on your deck with Scheme. In practice you will probably not choose to set aside Prince with a card that won't work well with it, and so will play the Action you set aside every turn from that point on. The set aside Action technically goes back and forth from being in play to being set aside each turn, but in practice it's easier to leave it sitting on the Prince and just announce resolving it each turn.
Prince has to be set aside to do anything; using Throne Room on Prince won't let you set aside two cards. The Action card you set aside has to cost $4 at the time you play Prince, but can normally cost more; for example you could play a Highway, then use Prince on a Laboratory. You do not play the set aside Action the turn you first set it aside with Prince. Playing the card each turn doesn't use up your normal Action play, and is mandatory; setting aside the Action when you discard it from play is also mandatory, you only fail to do it if the card isn't in play at that point. At the end of the game, Prince and the set aside card are returned to your deck before scoring. When you have multiple effects to resolve at the start of the turn - such as multiple Princes and certain duration cards from Seaside - resolve them in any order, and that order may vary from turn to turn; choose one to resolve, resolve it, then move on to another one, until they are all resolved. Cards which cost $0* such as Mercenary and the Cornucopia Prizes can be set aside with a Prince, as can cards from Guilds that cost $2+ or $3+ or $4+. Cards with a Potion in the cost cannot be set aside with Prince. Prince plays its Action on extra turns from Outpost and Possession. The Action card that Prince plays is in play after it's played each turn, so it will count for things like Peddler; Prince however remains set aside.
