Wednesday, April 13, 2016

Gauging combat challenges

In the comments of a fairly recent post, I was asked to describe how I judge the challenge level of a combat encounter.  Short answer is that I don't have any hard-and-fast formula, and more or less eyeball it.  But of course that only evades the real question, which is what do I look at when eyeballing in order to make a judgment?

Firstly, let me say that encounter balance, as fetishized in some recent editions, is abhorrent to me.  Crafting every encounter to be "level appropriate" takes the fun out of the game, in my estimation.  I don't like railroady scenarios with scripted highs and lows that require easy victories over mooks and dramatic nail-biting climaxes.  And no encounter should be a mandatory combat - if the players can talk, bribe, sneak, or trick their way past something, the DM absolutely should not nullify that to force them into Exciting Combat!™

That said, I also don't want to create dungeons full of killer encounters or boring cake-walks.  An adventure should include plenty of opportunities for winnable combats, as well as encounters that demand more discretion.  Balance, to me, takes place at the level of the entire dungeon or scenario, not zoomed in to the individual encounter.

The amount of damage a group of creatures can do in a round is, I think, the most important consideration in judging their threat level.  Two primary factors contribute to this: the damage potential of each attack, and the total number of attacks per round of the group. 

I would weight the total number of attacks more heavily. A fight against four goblins is likely to be more deadly than a fight against a single ogre because the goblins get four chances to hit every round, while the ogre only gets one.  Against a party of 1st level characters, the goblins could potentially kill four in a round, while the ogre can't finish more than a single one at a time, no matter how much damage it rolls.

Damage per attack I would judged based on how many attacks it would take to kill a typical PC.  The more rounds the party can stand against it, the less dangerous it is to them.  Can it kill a PC with a single attack?  An attack that just hurts a character is a prompt to make a choice: withdraw or fight on.  This is an important consideration because character death, if it happens, is more likely to be seen as a result of player choice.  A one-hit kill is just a one-hit kill.  If you want to give a 1st-level party a fighting chance to engage in combat without too much anxiety, make sure to have some monsters that do 1d3 or 1d4 damage around.

Hit Dice are the usual unit of Monster Toughness in old school games.  Dungeon levels are supposed roughly to correspond to the average HD of the monsters found in them, and BECMI and Rules Cyclopedia D&D even have an encounter balancing formula which is based on Hit Dice.  However, Hit Dice are a distant third in my estimation of monster threat level.  What they are is a fairly good indication of how long a monster will last in combat, and thus how long it will get to keep making its attack and damage rolls against the PCs. 

Hit Dice also affect the chances of successfully attacking, but only by about 5% per HD, which is a lot less than extra attacks do.  A 1 HD creature needs to roll a 14 or better to hit AC 5, which translates to a 35% chance.  A second attack increases the odds of getting at least one hit to 57.75%, better than having 4 extra Hit Dice! 

Quite often, big HD correlate with big damage, but not always, so it's still a good idea to gauge them separately.

All else being equal, a single high HD monster with multiple attacks is usually more dangerous than a group of lesser creatures whose HD and attacks approximate it.  Consider a pack of five 1 HD orcs with 1d8-damage weapons and a 5 HD owlbear with three 1d8 attacks.  Each orc will take 5 or so points of damage to kill, and each one killed reduces their number of attacks by one.  The owlbear gets its three attacks per round until it's dead.

Armor Class rates a little bit lower than Hit Dice in my Monster Threat Assessment.  It too affects how long the monster remains alive and fighting, but unlike a big pile of hit points, which can only be whittled away, AC is bypassed by a good attack roll, and a d20 is a lot swingier than most dice you might roll for damage. 

Special attacks are trickier to assess.  For low-level parties, their effect is actually minimal.  A failed save vs. poison might kill you, but so will a single good solid physical blow, and dead is dead.  The odds of missing a save and getting hit in combat are only a little bit different.  A save-or-suck power is similar to a low damage attack: it's a cue to rethink one's position, not instant Game Over.

Save-or-die and save-or-incapacitated powers become a big deal at mid levels, not because they become more absolutely dangerous, but because they're now a lot more dangerous relative to attacks that do hp damage.  An orc with a sword and a medusa with a petrifying gaze can both take down a 1st level character in one round.  Only the medusa is likely to be able to do the same to a 4th or 8th level character.  The character's hp increases almost always greatly outstrip saving throw improvements, and while healing spells and potions are by now fairly common, spells that will reverse the effects of poison and petrification are still either out of reach or in short supply.

By high levels, saving throws have improved enough to make the success rate of save-or-die effects acceptably low, and the party probably has access to remedies, which makes them an inconvenience rather than a deadly peril.

Of course, the number of attacks principle also applies to special attacks.  If a monster can direct its special attack form against multiple targets at once, or there are several of the monsters in the encounter, it magnifies the threat level in much the same way.

Lots of attacks > big damage per attack > high HD > high AC

Combinations of those factors are possible, naturally.  So, lots of attacks + big damage per attack generally trumps big damage and high HD;  big damage and high HD beats high HD and high AC, etc.  What about lots of attacks and high AC vs. big damage and high HD?  How do special powers change things?  Use your own judgment.  It's an art; not a science.

Putting It In Play

In practice, I try to balance a dungeon as a whole, with a lot of encounters that I think the party could handle without too much trouble, some that would be quite risky, and a few that would almost certainly be disastrous if handled with straight-up combat. 

Remember that a good fight is one that costs the party some resources to win, not necessarily one in which the sides are evenly matched.  To a wise adventuring party, evenly matched battles are to be scrupulously avoided except in the most dire need or the richest possibility of reward.  Evenly matched means that both sides are likely to suffer losses, and either side could end up defeating the other.  That might sound exciting, and it is sometimes, but an adventure is more than one fight.  It's a war of attrition.

In a good dungeon, the PCs might be able to win any given fight, but they probably can't win them all, one after another, in a gauntlet match.  Even winnable fights must often be avoided, in order to conserve resources for fights that are not merely winnable, but important and/or profitable.  "Can we win this fight?" is an important question, but so is "What about the next one?"

1st level parties are the toughest to plan for because, with their low hit point totals, outcomes depend heavily on the very swingy d20 attack roll.  1st-level characters and 1 HD monsters can go from full strength to dead with a single attack.  A seemingly even battle can become lopsided very quickly if one side has a run of lucky or unlucky rolls.  Additionally, if the party includes a spell-caster, the outcome may hinge heavily on which spell he has ready and whether he still has it or has already used it. 

If you want to design a dungeon for low-level characters in which direct combat will play a big part, encounters should be predominantly with numbers of monsters smaller than the PC party, with 1 HD or less, low damage potential, and poor ACs.  A few encounters can be with even smaller numbers of creatures with 2-4 HD and better damage or AC.  Anything bigger, tougher, or more numerous is a serious risk -- but don't let that discourage you from including a couple such encounters.  It ain't all about chopping things up with swords, and part of the fun is knowing the difference.

As characters gain in levels and hit points, they generally survive longer, and overall, combat becomes less swingy.  The more rounds they can go without dying, the more rolls are made, and the more rolls made, the more the cumulative result is pulled toward the average.  Characters with a few levels under their belts can go toe-to-toe with monsters well above their weight class more successfully than low-level ones can because hit points increase a lot faster than damage potential. That doesn't necessarily mean they'll win, but an ill-chosen fight is less likely to wipe them out before they can even realize their mistake and run away. 

Still, I think it's good to follow the rule of thumb that the majority of encounters should be ones that the party could handily best in combat, but will take a bite out of their resources.  The more fights they pick, the more their resources and hit points get ground down, the closer they get to being that 1st-level party all over again, when life and death can hinge on a single misguided choice or bad roll of the dice... 


  1. This comment has been removed by the author.

    1. You could add consumable magic items and charges to that list of resources potentially depleted in combat.

      The 15-minute adventuring day could be tackled either by making the passage of time more meaningful (see my post on Time as master resource) or, as I think you're suggesting, giving magic-users a little more to work with. Spell point systems have always felt "off" to me in play - it tends to put the focus on math rather than magic in my experience. YMMV. I'm playing with the idea of 0-level spells, usable at will, with effects that are trivial but potentially useful to creative players, so the MU doesn't feel quite so useless after firing off his one 1st-level spell. Ideally, I think I'd do both.

      Your observation about danger of ogre vs. goblins depends to some extent on edition and house rules. With B/X played straight, a 1st level fighter will average about 5 hp; goblins do 1d6 damage and ogres 1d10. The ogre is more likely to score a kill, but a goblin still could too. If you're talking AD&D fighters with d10 hp, or a max hp at 1st level house rule, then you're right; only the ogre stands a chance of a one-hit kill. In that case, I'd agree with you that the ogre is the greater threat. So, adjust your assessment accordingly.

      I don't like raise dead and usually house-rule it out of existence in my games. I'm not sure how I'd handle it if I did allow it -- Complete body required, or maybe just complete skeleton, with appropriate disabilities if any limbs are missing? Resurrection from a single bone would probably be a job for a more powerful spell. It really depends on your particular tastes regarding how easy or difficult you want it to be to bring back the dead.

      Perspectives are always good to have! I know I've changed my position on some issues I never thought I'd budge on after reading someone else's take on it in a blog or forum.

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    1. I've never really had much interest in delving into the behind-the-scenes strife, so I couldn't speak to those motives at all. I think Moldvay Basic was an update to the Holmes rules, which in turn were an update of the original D&D game. It seems likely to me that race-as-class evolved from OD&D, in which elves could toggle between fighter and magic-user, and dwarves and halflings were limited to the fighter class. B/X tidied up the elf into a full-time combo F/MU and made dwarf and halfling "fighters" into their own classes distinct from human fighters. For a basic game, that seems a neater package than a lot of race-class combinations, and I never minded it. Granted, that was the way I learned to play, and wasn't aware of separate race/class until later. I'm pretty sure 1d6 for all weapons also originated with OD&D, and variable weapon damage was introduced in the Greyhawk supplement. Moldvay included it as an optional rule, and I expect most B/X players used it, as I did.

      My understanding is that AD&D was meant as a tournament rule set, with established rules for many more situations than OD&D and the Holmes/Moldvay branch of the game.

      Incidentally, the Labyrinth Lord Advanced Edition Companion (AEC) does a pretty nice job of bolting some of those AD&D innovations like separate race and class onto a B/X-style chassis.

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    1. I'm not sure I'd go that far, especially considering that some 1st level magic-user spells are pretty powerful. It might be a tad unbalancing to have a rookie mage able to throw three or four sleeps spells in a day.

      Character death in my games is probably a lot less common than in many old school campaigns, but it does happen. I'm a big fan of foreshadowing danger. There's plenty of opportunity for players to get their characters killed if they're not careful, but they'll see it coming if they pay attention. The decision whether or not to open the next door is a lot more interesting if they have reason to believe that something very nasty is waiting behind it than if it looks just like any other door in the dungeon.

      I think it's also important to cultivate the players' trust that I'm not going to nullify their plans in order to force them into combat, or punish them for trying to escape when they're overmatched. They know that if they try to bluff, trick, or bribe the monsters, their choice will have an impact. It may not be exactly the result they were going for, and it may not be an unqualified success, but very rarely will I simply say, "No, that doesn't work. Roll for initiative!"

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    1. All your proposed modifications to the sleep spell are worth considering. I've been pondering making it a single-target spell, but scaling with the caster's level to affect more powerful creatures.

      I think spell points work perfectly fine in computer RPGs, but my experience trying them in D&D was less than satisfying. "Fire and forget" always ground my gears a bit too, though. For me, the happy medium seems to be a spell slot system. Memorized spells stay memorized, and you have a limited amount of power per day to cast them, but instead of an amorphous pool of spell points, you have a certain number of "slots" for each level of spells you can cast - 1st level slots for 1st level spells, 2nd level for 2nd level, and so on.

      It would have been interesting to see what Holmes would have done with a spell point system. The idea of spells scaling with level, and the infamous sleep spell, may not have survived in their best-known forms. If a 10th level wizard could throw five magic missiles per spell point, why would he ever spend three points to cast a 10d6 fireball?

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    1. 1, I think deserves a post all its own, which will be forthcoming soon.

      2, I don't really have a mathematical formula. There are just too many variables in play to be that precise; thus, eyeballing it. I'd say 60/40 represents a fairly costly fight, though. I think it's good to have some of that level, but more in the 70/30 range feels about right.

      3, I just wrote a post about the trend toward scripted adventures and massive rule sets to express my thoughts on that topic. You might find it interesting.