Dominion: Prince was released at Origins 2014.
You may set this aside. If you do, set aside an Action card from your hand costing up to 4. At the start of each of your turns, play that Action, setting it aside again when you discard it from play. (Stop playing it if you fail to set it aside on a turn you play it).
For further information on this set: http://boardgamegeek.com/boardgameexpansion/160943/dominion-prince-promo-card
Due to publisher request - these will be limited to 1 set per customer