Buffy and Spike get sucked into or recruited into some kind of game? Any type. Like amyxaphania's The Game.

In case this is a different story than the one you referenced:

The Game by Saber ShadowKitten

Summary: Buffy and Spike, and later the rest of the Scoobies, get unwillingly involved in an inhuman "Game" in which only the best of the participants survive.



This story isn't so much a game as a cursed story book that Spike and Buffy get drawn into and cannot get out of until they complete the story, so in that sense it is kind of like a game. There is a set 'script' if you will that they must follow in order to move forward in the 'story':

A Pirate's Life for Me by Addie Logan

Summary: As the Slayer, Buffy Summers is certain she hates the vampire Spike. But when an enchanted book pulls her into a world where she's Lady Elizabeth Summers, trapped on the ship of famed pirate William the Bloody, things start to look a little different...