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The frost wyvern is a fine idea. Although I've got a (very) rough idea of the immediate area of the game world I wanted, with this one, to have lots of blank space for player input. About the only big rule I can think of is that there are no hordes of evil humanoids (the ur-men are a major exception), otherwise pretty much anything that you'd find in a Conan-type story will do.
From Mastering Iron Heroes, which covers the kind of things I'm hoping for:
CREATIVITY ON THE FLY
Sometimes, working out all the details of the game world before you start stunts your creativity. Rather than commit to the details of a region before the game starts, allow the players to flesh out their characters’ homelands in response to actions in play. This can lead to unexpected developments, especially if the players pull details out of thin air without thinking about
how they fit into the world as a whole, but it also makes the game far more flexible. Sometimes, interacting with others in a shared creative environment spawns ideas that are more fun and interesting than when you work in a vacuum.
When players create ideas on the fly, they should ensure that the new details are germane to the action. For example, the weapon master Mbenga and his thief companion Darla sneak into the gardens outside a baron’s palace. There they spy a panther stalking through the trees. Mbenga stops in his tracks. “Panthers are sacred to my people,” he whispers. “I cannot
raise a weapon in anger against one, even if my life is at risk!” This example is a bit extreme, but it illustrates the type of cultural detail you can add to a game as play progresses. Mbenga’s player might note further that his people consider panthers to be heralds of their god of war. What was a simple encounter now becomes more challenging, because violence is no longer an option. This scene makes the important traits of Mbenga’s culture more compelling and memorable.
In comparison, if you as the DM created that detail ahead of time, it would be up to you to work it into an adventure. With all the other preparation needed for the game, the detail might have been lost in the mix. Giving the players more narrative control lets them contribute to the game in new and imaginative ways. Remember, though, that with such narrative power comes the responsibility to keep the game enjoyable for everyone. It might be fun
to declare that your character can’t take on a particular opponent, but it also could make the game less fun for the other players and the DM. When you add an element to the game, make sure it doesn’t bring the action to a screeching halt. In the example above, Mbenga’s player might wait to see if he can get past the panther without violence. The peaceful path might be riskier or harder than simply attacking the animal, but the game can continue. However, if the DM had expected Mbenga to fight the panther and hadn’t prepared for other courses of action, the player’s choice could derail the game.
This option isn’t for every group. It’s best suited to players and DMs who are used to coming up with ideas on the fly. Everyone should feel comfortable dealing with a sudden change in the game. This sort of creativity works best if the players aren’t self-conscious about breaking the game. Finally, consistency is still important under this model. As players flesh out the PCs’ backgrounds and homelands, they should take notes. The DM and other players might build on what one person creates, and it isn’t fair to change facts without telling them. You might reveal that a detail was a lie or myth, but don’t do so after a player added another feature to the game under the assumption that your detail was true.
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