I use a deck of these Storytelling game cards:
Atlas Games: Charting New Realms of Imagination
I deal 3 to each player at the beginning of the session, they are allowed to trade amongst each other and each player may play 1 of the 3 cards. I deal a new set of 3 cards at moments I deem appropriate, scene transitions, or a couple encounters before a big boss fight, etc.
It is up to the players to interpret what a card could do and as long as their reasoning is somewhat sound pretty much anything goes. As the DM I reserve the right to say no if an interpretation is to far out there.
Some examples of the cards are sword, fly (like flying not a fly

), parent, enemy, storm.
Some examples of the cards in play:
- The sword card has been used to make a miss into a hit, confirm a critical, aid in disarming an opponent
- The poison card was used to slip something into a drink to knockout a player who was gambling away the parties money at a party (in this case it was the mage playing the card so I said ok since he has some knowledge of nature, had it been the fighter who has no knowledge of nature I most likely would have said no)
- The storm card was played to bring down a torrential rain storm to obscure the parties tracks as they were being tracked by a group of orcs
- The fly card was played during a game so that by a ladder happened to be near by when the players needed to scale a castle wall.
About 1/4 of the cards are unusable as they are cards related to the Story telling game itself but the other 3/4 have a picture and a title related to fairy tale stories, which, with a few exceptions, are also themes/items that appear in the fantasy genre. It also comes with some blank cards so you can create your own cards.
The art is good, the fairy tale style may not appeal to some, there is also a dark fairy tale expansion that adds more, darker, cards.
You can see an example of some of the cards for the basic game here:
ONCE UPON A TIME A story telling game
I have found these cards work really well for my group, they like having the option of playing their cards in combat, or to change up/modify/interact with the story in interesting ways, it keeps me on my toes and it gives my players another way to interact within the game.