So my last session was 15 hours long and features a 12+ hour fight. The entire fight was tense from start to finish.
One of the commentators on that session's writeup, Lars L, asked about how I balance such encounters.
The short version is that I don't balance fights. That this one was such a balanced nailbiter was more luck than anything else. My experience told me this fight would be tough, or at least could be tough, within a certain range. But it could have been a short fight with a few lucky rolls by the PCs, or bad ones by the lizardmen. It could have been a TPK or a walkover, but it was tough enough that the latter seemed unlikely but not so overwhelming the TPK seemed likely, either.
The long version is that, like everyone else, I do balance fights - I gauge the relative challenge of the encounter with how much of an impact I'd like it to have. That does come from experience, not from luck.
So let's talk about that lizardman / PHB cover homage fight. Over 80 bad guys, ranging from fodder's fodder to summon creatures and badass leaders backed by magical support.
This fight was set out a while back, and while the lizardmen learned and adjusted from the repeated skirmishes they had with the PCs, it stayed about the same. They armed up as well as they could. They set plans to call in reinforcements and send a flanking force (one champion and all the guards, etc. he could sweep up on the way, plus a summoned creature). They tried to fight in combined units (lizardmen, acid slorn, and newtmen together) not separately. They pushed when they had to but generally tried to keep their advantage on the defensive. That it didn't work has a lot to do with generally smart play by the PCs and their general man-to-man superiority.
I certainly ran the NPCs with vigor, and bad intentions. They wanted the PCs dead and used the best tactics they could do kill them. I always play my NPCs this way - they fight as if they want to live and they fight with intent to kill (or capture, or escape, or whatever - as appropriate.) I don't pull punches or sacrifice NPCs to make the PCs feel better. My players know this, which makes every fight a bit tense.
After the fight Dryst's player and I talked about it as we cleaned up (me my minis, maps, and PC; him, wiping the battlemat for me.) Had Christoph the Scout also been there, or if Borriz was there, or Honus - basically, if there was just one more PC-level delver - the fight would have been much shorter. Or if Dryst had just a few more paut potions or a bigger power item. Or if Galen had a spare bow once his broke, instead of needing to waste turns scrounging up a tiny shortbow to plink with. We both figure the fight would have been much shorter and lopsided in favor of the PCs.
But had the PCs been a smaller group - say, had Dryst and Honus smashed the door guards with ease a few sessions back and managed to force the door and get into the temple - it would have probably been a TPK.
Had I just stuffed some lizardmen in the room, it would have been a walkover. Instead, I modified the environment to make it more interesting (bad footing, chances to fall, wet air, special supernatural modifiers, no morale checks except under certain circumstances). I also made sure the opposition was appropriately tough. I also made sure I had some idea of how they'd fight and what they wanted to accomplish. These are all things I might not do for a trivial monster encounter, at least not to the same degree.
So really, I say I don't balance fights, but that's not quite true. It's better to say I don't decide which fights I want to be epic, I just set the stage for that potentiality.
I don't balance the fights so it all falls to clever PC tactics and good die rolls, but I make the fights appropriately challenging enough that this could happen.
And I don't decide what the outcome or costs of a fight will be, I just place it and scale it so it's worthy of the time it takes to play out.
So yes, you can call that balancing the challenge. This is actually pretty old-school - if I say "Level 1 of the dungeon" and you say "rats, kobolds, and goblins" then you know what I'm talking about. You just don't put encounters down willy-nilly, there is some kind of external balancing factor. This is especially true for a "Saturday night special" - a special placed encounter, meant to be a real challenge. You might just write down "3 trolls" for a room and figure it'll be tough or it won't, but for something meant to be special, you just can't do that.
To gauge this does take some experience with the game system, or one that has a great deal of balancing built in (such as every edition of D&D I'm familiar with - see level 1 and giant rats and kobolds all the way through Challenge Ratings in 3.x). In GURPS it can be trickier, since points provide equality of choice, not balance of results.
My advice is to play as much as you can, but also to draw off the experience of others:
- the excellent advice on fodder/worthy/boss level monsters in DF2.
- The various Melee Academy posts, so you know what's what with the combat options in front of you.
- My two posts on making tough DF fights - the original and the more recent minor expansion (also read the comments on that one).
- Doug's post about skill levels in GURPS. Don't be shy about giving monsters in DF skill 18+, as they may need it to even concern high-defense PCs and fend off feints, Deceptive Attacks, and so on.
Also, I can't find an appropriate post to link to, but Sean "Dr. Kromm" Punch has written often about making some "fights" not about combat. Time limits, stop-the-ceremony situations, unkillable monsters who can only be dealt with via some unusual means (break the soulstone, kill the demon - meanwhile he's kicking your ass), puzzle monsters (ahem, Acerak), obstacle monsters, etc. can help make for interesting and memorable encounters. Everything doesn't have to come down to whittling down HP.
Remember that if the encounters are always scaled to your PCs, and balanced against your PCs, and you'll win by the skin of your teeth if you play well, you know everything is potentially winnable. Nothing is a walkover (or looks like one) because you know there aren't any. But equally nothing is a TPK waiting to happen because it's never too hard for you. That's fun for the one fight, yes, but it's not as fun as an epic that just happens organically, in my opinion.
So the short version, after all, is this. Learn how to make the fights potentially interesting, but don't try to balance them. Make them something that could be fun, let loose, and see what happens. But yes, definitely figure out how to make them appropriately challenging.