In the game of WyshMaykers, characters can make anything they wysh come true. Anything. Because Anything is such a large swath of possibilities, two things had to be ingrained in the game system: Creativity and Ambiguity.
Becasue anything is possible with a Wysh, we really kept the game mechanics light. Or rather, we used the light game mechanics from -U- the Game of Stories. See, in core game of -U-, there aren't a lot of crazy modifiers or target numbers or difficulty charts and whatnot. Characters just get a number of chances to succeed at things and roll dice to see if they succeed or not. That fit really well into encouraging the open creativity of the game that we wanted to have. We wanted players to be able to shock one another with the crazy things that they wyshed for. We wanted Story Referees to try to account for wyshes that might unbalance the game. We wanted players to have to react to the unexpected using their mind, their stats, and their dice. The lack of heavy math and terribly complicated charts lent itself to this free-flowing no-holds-bared experience very well.
As we played the game, it became apparent that sometimes it was nice to have something mechanically that the Story Referee could use to limit the players in some way. We came up with the optional Modifiers table. With the modifier table, Story Referees could reduce the number of chances a character had to succeed at making a wysh. Some of the restrictions were easily identified (number of people affected). Some we left ambiguous on purpose (like complexity and beleivability of a wsyh). The ambiguity worked well and allowed the Story Referee to justify and control the flow of the story in the face of creatively destructive players. This then fed into the the creativity of the game even more as it allowed Story Referees the chance to be creative in limiting players, and players a new boundry to be creative within.
Both Creativity and Abmiguity play into each other heavily in WyshMaykers. Give the game a try: http://rpg.drivethrustuff.com/product_info.php?products_id=94202&affiliate_id=229603