The idea for an expansion for Bang! with a funny tone, sporting characters and effects more wild than balanced (somewhat like Magic: The Gathering's Unglued expansion), was airing in daVinci's minds by several years: as early as 2005, a set of characters with names inspired by playtesters and daVinci executives was proposed: characters like Dominic D.G., Rob Corbell and Emily Sharr, and cards such Bean Pot (recover 3 life points) or what is now called the Lady Rose of Texas. But such an expansion obviously required a large base of aficionados, because a parody is more appreciated when its stereotypes are widely recognized: so the whole project was stopped until 2009, when a mini-expansion with bizarre characters was proposed, maybe to be handed out free on special occasions or events. After some brainstorming, "wild" cards, too, were added to the project, triggered by a mechanic similar to the well-tested one found in High Noon and A Fistful of Cards.
During playtest I used for the characters the mangled names of famous Western movies actors, which are still in the final product; while other cards had names of famous Wild West women, some of them can be recognized still now, i.e. Elena Zontero and Sacagaway.
Naturally, a "wild" expansion does not mean an "unplayable" expansion: from the beginning, the clear aim was to make something stretching the game balance at its maximum, but not more. The main direction was: "funny effects; and if you are unsure whether an effect is balanced or not, say yes".
Since I don't want to do the same things again and again, I did not choose to use the exact same mechanic found in High Noon (a card for each round, turned by the Sheriff): I chose instead to revise it lightly, making the new card effects with less predictable duration and more lasting effect. In addition, I willingly left the most devastating effect - which clears out all the roles, transforming each player into a Renegade! - as the last card, which is appropriately very difficult to reach to avoid players playing as Renegades from the beginning.
The choice of new characters was longer than I thought: some of their abilities was really funny to read and "wild" to the right point, but they proved dull or boring to play, or they started deadly loops. Some of them, on the contrary, was balanced from the beginning, like Big Spencer which is my favorite character above all: he could be included without problems even in a "serious" expansion. Other characters surprised all playtesters: for example, nobody could tell a priori that John Pain is so powerful.
It is right that some particolar situation is left to players' intuition, experience and common sense to be properly sorted out (at least before compiling an official FAQ), but keep in mind that such an expansion is aimed primarily to expert players, who won't find too difficult to understand the gaming idea behind each card.
Among others, the effect reflecting more accurately the whole expansion is Gag: it is very funny to see players moan and gesture because they cannot speak - someone even stops other players from answering to the phone, while others gleefully pay a life point just to publicly argue with another player which is playing badly…
The first name for this expansion was Wild Wild West, but in the end, to avoid legal copyright issues with the movie and the serial with the same name, it finally became Buffalo Bill's Wild West Show: most importantly, the Wild word remained in the final name of the game.