No matter the venue being used for story telling, set pieces seem to be a common staple. Especially in the action and adventure genres of stories. It isn't surprising really. Stories are designed to build up to a climax, and the climax is supposed to be the most exciting part of the story, so it kind of goes without saying that that scene is going to be big and special in its own way. It has to deliver on all that excitement after all. Other set pieces, usually, represent the other peaks we hit on the way to the main climax. Little mini climaxes hit before the rest periods as we work up to the big finish. RPGs, it may or may not surprise you, are no different in having these set pieces. The question is though, how do you make the most of them?
A Different Kind of Set Piece
Combat, and just about everything mechanical, in RPGs can tend to get a bit bogged down with the mechanics of the game. This isn't necessarily a bad thing, but it can get in the way of the tension and excitement that a set piece scene in a movie or book might bring about. So, instead, these set pieces in most RPGs are done a bit differently, and borrow heavily from our friend the video game. That's right, I'm talking about boss fights.
Boss fights are usually, by definition almost, a set piece battle in and of themselves. The boss is large, powerful, and quite often has some special mechanics or trick to beating them. There is something different about fighting them, and it is more than just "Reduce to 0 HP to end Segment 3 of Story 2". This brings up a tension all of its own, because people know that they're fighting the big bad, and the big bad isn't the big bad if it isn't capable of killing a player or two, now is it?
Because of this, these fights are usually where players will unleash their saved abilities. Even players who usually hoard their items, or carefully ration out the charges on their wands and potions, will use them with a bit more frivolity. Once again, this is the big bad after all...
A Narrative Look
But what is happening in that frivolity? Think about it for a second. The PCs are going to down, they're throwing dailies, hourlies, non-renewable charges, and everything else they can think of at this big bad. The mages are dipping into their bag for not just the big spells, but for the really big spells. Fighters are swinging for the fences, and the rogues are diving from the rafters to try and squeeze out just an extra point or two of damage. Yes, this is all going down slowly and methodically with the mechanics, but look at it from a narrative point of view. Most systems use a 6 second round timer, and anyone who thinks about what just happened this round is going to see that.
The point of this? Basically, I'm just showing you that what you want to happen in a big set piece scene is there already in what the mechanics represent is going on. That means that all you need to do is pull that feeling out, not add it in. Keep that in mind.
The Set Up
A set piece can be a set piece without any set up, but the truly great ones have a build up to them. Luke's confrontation with Vader in Return of the Jedi is all the more memorable because of the confrontation in Empire Strikes Back. Even that is made dramatic by all the build up given to Vader up until then, including the fact that Luke only survived their first one-on-one run in, because Han came in to save the day. This is true in most stories, and even in most games you'll play. The big set pieces, the really awesome ones, are like that as much because of the build up as they are because of what is going on.
Because of this, you want to give some lead up to what is going on. A pre-final show down encounter with the big bad (however dangerous that may be with the ever illusive insta-kill critical hit lying around) is a good, and perhaps even a necessary thing at times. If nothing else, giving the players the feeling that they've lost to this person before can work wonders. (For some reason, PCs hate being beaten...)
The execution here is fairly self explanatory. Your plot leads up to a big set piece, you then have the set piece. However, how you handle it is going to depend wildly on your gaming group. Some groups are going to want to stick to the mechanics, letting the fact that the big bad is a big bad mechanically do the talking. They'll just have to reminisce afterwards about how awesome it was when the 6D6 Fireball rolled max damage and totally wiped all the henchmen out. Other groups are going to want to go a bit faster and looser with the rules, and play up the drama and tension that way. It is less about the mechanics specifically saying heroic sacrifice will let someone kill the bad guy, and more about the GM being like "cool, I'll allow it!" at the right moment.
Personally, my style falls in the middle. I try to stick to mechanics, but also let what the players are doing affect things. Maybe that makes me a big softie, but a heroic sacrifice just isn't as cool when it does nothing in my book. As for how I try to keep narrative tone with the mechanical focus? When I can, and when I remember (harder in a big game, easier in a small game) at the end of the round I sum up what happened and try to make it sound a bit more exciting with descriptive words. Leave the numbers out of it, and just use the description to set things for the player's imagination.
Like everything else about RPGs, there are as many ways to do this as there are GMs out there trying it. So, what tricks have worked for you over time?