This blog entry might contain spoilers.
I got reacquainted with the Whodunnit comedy film Clue earlier this week. In case you're unfamiliar with that movie, it's adapted from the classic Parker Brothers board game (back in the days when movies based on board games were clever and memorable) and was originally released in theatres in three different versions, each with its own unique ending. Each version can be viewed on the DVD, either with all three resolutions shown one after the other at the film's end or with just one resolution that the DVD randomly chooses.
The three endings go as follows: In Ending 1, one of the six suspects turns out to be the murderer, who also had some help from an accomplice before adding them to the body count. In Ending 2, another suspect who worked entirely alone turns out to be the murderer. In Ending 3, every suspect turns out to have killed one person each over the course of the film. While none of these endings makes total sense, I've always liked the version where everyone is guilty the best. Not only does it take the film's over-the-top-confusion motif to the maximum, but it also feels truer to the original board game, where every suspect has been the killer at some point.
In contrast, another Whodunnit comedy film called Murder by Death plays with our murder mystery expectations by revealing that there was never really a murder at all -- maybe. That's another confusing one. Either way, none of the detectives involved ever wins their host's contest by solving the case and identifying a culprit. In both It's a Mad Mad Mad Mad World and Rat Race, none of the parties chasing after the cash prize ends up winning it. These resolutions again create unification and balance in their overall stories and ensemble casts by not suddenly favoring one character over the rest.
All-or-None endings are also popular in "Versus" movies. The assumption going into a film called Mega Shark Versus Giant Octopus is that one of the over-sized sea monsters will defeat the other by the end, much like how a boxing match has a clear winner and loser in the final round. Instead, Mega Shark and Giant Octopus kill each other at the same time and there's no winner at all. Pokémon: The First Movie builds up to a huge throw-down between Mew and Mewtwo, but both characters end up deciding to call it a draw because they're too evenly matched for one to defeat the other. This could be a case of a fight having either no winner or two winners, depending on how you want to look at it.
Even when films like this do pick a victor, they don't always commit to it. Films like Freddy vs. Jason, Alien vs. Predator, and a large number of Godzilla movies end with a last-minute hint that the loser is or could be a threat still. This seems to be a trend for two reasons: 1) It leaves the film open for sequels, and 2) it keeps the film from totally disappointing and alienating fans of the defeated character. While this may be a more cynical view of All-or-None endings, these movies are still aware that both of their titular combatants are equally important.
So what am I getting at with all this rambling? Mainly that the All-or-None ending has a place in storytelling even if it may seem indecisive at first. It's always important to have a clear hierarchy of importance in mind for your characters when you write, and in cases where all of your major players are of equal importance, suddenly shifting most of the attention to one of them at the end can feel a bit out of nowhere and arbitrary.
If you properly set one character apart from the rest throughout the story, perhaps by telling it from their point of view or by giving them the most emphasis in each scene, then making them the focus of the ending would feel a lot more natural. That's not to say that this rule can never be broken, but it's usually best to clearly set something up before paying it off. Otherwise, a lot more stories might come with multiple, interchangeable endings that don't always add up -- and that doesn't fare well outside of comedy.