Thursday, December 22, 2016

Dwarves and magic

The dwarves of yore made mighty spells,
While hammers fell like ringing bells
In places deep, where dark things sleep,
In hollow halls beneath the fells.
                    --J.R.R. Tolkien, The Hobbit

Dwarves in most old school versions of D&D are described as being highly resistant to magic and having no aptitude for it themselves.  OD&D dwarves are always fighting men.  B/X and BECMI have dwarf race-classes that don't allow for magic-use.  First edition AD&D says, "Because of their very nature, dwarves are non-magical and do not ever use magic spells" and then contradicts that statement with a note that dwarf clerics exist as an NPC class only and may attain level 8.

Literature and folklore, of course, have not always portrayed dwarves as non-magical beings.  Even Tolkien, whose dwarves are arguably the archetype for D&D dwarves, seems to imply otherwise, as illustrated in the quote above.

Second edition AD&D made cleric an option for dwarf player-characters, and the Dwarves of Rockhome Gazetteer added a BECMI dwarf-cleric class.  The BECMI dwarf-cleric was essentially the same as its human counterpart, but with dwarf saving throws, axes and hammers instead of blunt weapons, and minus the ability to turn undead.  The Gazetteer also provides rules for dwarves to craft magical weapons and armor, as befits their reputation of master smiths.  I think some later editions of D&D have even opened the magic-user/wizard class to the dwarf race, but once again, that's no more than saying you're basically the same as a human magic-user, but you're short and live underground.

I'd like something that feels a little different from human and elf spell-casting, something that makes playing a dwarven spell-user a special experience.

But what should dwarven magic look like?  What should it do?  How do dwarves invoke magical power?

My first thought is that their magic should be limited to the things traditionally associated with dwarves -- elemental earth (stone, metal, gems) and elemental fire (the forge.)  They shouldn't be able to, say, charm people or turn invisible or polymorph themselves into animals, but they absolutely should be able to shape stone or make it transparent, heat or cool metal, mend or break metal or stone objects, and so on.

I'd probably make dwarves only able to affect earth or fire materials directly.  For instance, a dwarf spellcaster could cast resist fire on a suit of plate or mail armor, and it would protect the wearer, but he couldn't cast it directly on an ally, nor on a suit of leather armor or wizard's robes.

How does a dwarf go about casting spells?  Tolkien's line gives me some ideas.  Rhythmic, sonorous chants are one possibility, or perhaps one element, of dwarven spellcasting.  Hammers falling like ringing bells is the other.  Perhaps a dwarf needs a hammer with which to strike the item he wishes to enchant.  This wouldn't just be a symbolic or ceremonial striking, but striking in a precise way and a precise number of blows to create whatever magical resonance is desired.  This might make many spells take longer than a round to cast, and pretty much eliminates the possibility of ranged effects, and I'm comfortable with that.

All of this probably entails creating a new spell list, possibly utilizing existing spells from various editions and completely new ones.  I think I'll soon be combing through spell lists and pondering unique new effects to compose such a list.

Thursday, June 16, 2016

Quick thought on wandering monster checks

A very short post today.

In B/X, the rules specify rolling for wandering monsters every other turn in the dungeon, with a 1 on 1d6 indicating that an encounter will take place next turn.  For whatever reason, I always had trouble with this "every other turn" procedure.  I'd forget whether I had rolled or not last turn; sometimes I ended up rolling several turns in a row, and sometimes I'd skip several turns, distracted by more pressing matters.

Well, wait a second - we've got that seldom-used d12 just lying around.  How about rolling every turn, with a 1 on 1d12 indicating an encounter?  The odds aren't quite identical, but are within 1% of being equivalent to 1 on 1d6 every other turn, and it's one less thing I have to remember from turn to turn at the game table.

Monday, June 13, 2016

The art of picking a pocket

Of all the classic thief abilities, the one that seems to see use least frequently in my games is Pick Pockets. I blame the rather unimaginative name, as well as some misconceptions that I and my players have held about the ability.

As a young DM, I saw pocket picking as an act of stealth: You sneak up on someone, and if you manage to do so unnoticed, you carefully fish about in his pockets.  This, obviously, made it extremely difficult to pull off a pocket-picking, because it inevitably required a Move Silently roll to get close enough to the target.  Making one roll with a relatively low probability of success is bad enough; requiring two made it essentially pointless even to attempt.

But the classic pickpocket operates in a crowded marketplace, not a dark dungeon, and probably the most classic ploy is bumping into someone and surreptitiously relieving him of his valuables while pretending to apologize and dust him off.  That's much less about stealth and much more about manipulating the target's attention and perception.  Through a combination of words, gestures, eye contact, and other subtle techniques, the thief draws the mark's attention where he wants it, and away from what he's really doing.

What else might a thief do with such a talent for misdirection?  Planting an item on the mark is an obvious possibility -- the reverse of a traditional pocket-picking.  A sneak attack for double damage, a.k.a. "backstabbing" is another one.  A good line of patter keeps the target from noticing the dagger which the thief intends to stick between his ribs.  If the thief is good enough at it, he might even be able to pull it off in a crowded room without giving himself away.

Simple faux-magic tricks (i.e. prestidigitation) can be carried out with panache, as can all sorts of variants of the old shell game.  Switching a desired object for a worthless replacement right under the nose of the owner?  Absolutely.  Need a lock of someone's hair for some nefarious alchemical purpose?  Roll the dice.  Slipping poison or a sleeping draught into a goblet of wine?  Yep, that too.  Or maybe you'd rather save the king's life by switching his poisoned goblet for a safe one, without making a big scene.  Same principle applies. 

As DM, I'd ask the player for a general description of the character's "cover" -- what's his excuse for getting close to the mark and what's he saying or doing to divert attention and suspicion while he works?  Maybe he's flirting, or pretending to admire a piece of jewelry worn by the mark, or chatting with her about the artistic merits of a painting they're gazing upon.  If it seems decently plausible, roll the dice and see if he succeeds.

"Pick pockets" strongly implies that the ability is only good for picking pockets, but the same set of skills that allow a thief to lift items off an unsuspecting mark are useful for a multitude of other sneaky things as well. Terms like sleight-of-hand or (my new personal favorite) legerdemain are much less constraining, encouraging more imaginative use of the technique.  Pretty much anything a player can think to try that involves diverting a mark's attention away from some small manual task could be considered an application of this versatile skill.

Wednesday, April 27, 2016

The continuing evolution of Goblins & Greatswords

It's been a weird few months, with occasional crests of mental clarity and deep troughs of frustratingly impenetrable brain fog.  For most of that time, my fantasy heartbreaker project, a.k.a. Goblins & Greatswords, has been relegated to a back-burner position and left to simmer.  It turns out that back-burner simmering is good for gaining new perspective on things.  This is mostly a thinking-out-loud sort of post; nothing's set in stone.  Any comments or insights from other minds are welcomed and encouraged.

First off, I'm thinking of shooting one of the most sacred cows of D&D-like RPGs: The d20 combat attack roll.  Instead, I'm looking at a roll of 1d12 plus an exploding weapon die. (Whenever the maximum is rolled on the weapon die, roll again and add to the total.)  Weapons that are difficult to use or have weak armor-penetrating ability get a smaller weapon die, like a d4, while those that are easy to use and/or good at breaking through armor get larger dice, i.e. d6 or d8.  Damage would still be capped depending on the weapon type.  As before, the objective is to beat the target's AC (ascending), with one point of damage scored per point the roll exceeds the AC, up to the cap. 

The most basic system would be to simply assign d4, d6, and d8 weapon dice to light, medium, and heavy weapons, which would have damage caps of 4, 6, and 8 points respectively.  An advanced option might assign weapon dice and damage to each specific weapon type.  Thus, you could have weapons that are relatively easy for an untrained combatant to use but less damaging, and weapons that require more skill to handle but potentially deal bigger damage.  Maybe a war hammer uses a d8 weapon die, with max damage of 4, while a sword uses a d4 and max damage 8.  A good all-around weapon might be d6/6. 

Monsters would probably just use d6, with their Hit Dice accounting for most of their combat ability.

This is, in principle, quite similar to simply adding flat bonuses or penalties to attack rolls, but using an extra die instead injects a little more randomness.  It's also, I think, easier to remember than a + or - modifier to a roll, because it's an integral part of the roll, not something tacked on as an afterthought -- though maybe that's just me.  And hey, finally the d12 gets some serious love.  We're talking one of the game's most often used mechanics.

It also introduces some potentially useful and interesting quirks.  For one, characters attacking unarmed obviously wouldn't roll a weapon die with the d12, so unless they're highly skilled fighter-types, they probably won't have much success punching a guy in plate armor (AC 16.)  That seems like a good thing to me.  It also means that grappling a weapon-user is more difficult, even if the opponent is completely unarmored, since achieving a grapple requires beating the opponent's combat roll, not its AC. 

Also, with two dice in play, there are at least four different "critical" conditions.  Rolling 1s on both the d12 and weapon die makes for a critical fumble of some sort, typically resulting in loss of the next combat action.  A 1 on the d12 and max on the weapon die might mean the weapon breaks.  A 12 on the d12 is a critical hit -- damage is uncapped! If the weapon die explodes on the same roll, the target could be in a world of trouble.   

Outside of combat, I'm rethinking how thief-like skills could be handled.  A binary pass/fail roll isn't usually very exciting, and there's not much player agency involved.  Could thief skills be reworked to be more exciting and engaging?  Maybe.

Let's scrap the percentages, and instead express skills as a simple bonus, ranging from +1 at 1st level up to somewhere around +12 to +16 for level 15.  Expressing it as a bonus implies that the character is just better at things that anyone can attempt -- starting off only slightly better, but eventually completely outclassing the untrained.  That's a pretty good parallel for combat, which the rules allow anyone to do, but fighters are just better at it. 

Want to pick a lock?  Any fool can try, but a character with some skill at Tinkering has the best chance.  Roll a d6 and add Tinker bonus, if any.  What do you need to roll?  Depends on how good the lock is.  A cheap lock takes a 5, a good one a 10, and a masterful one a 15 or even 20.  Didn't make it on the first roll?  Keep trying, if you've got time to burn!  Each attempt takes a full turn, but the rolls add up.  Just don't roll a 1 -- that wipes out all your previous progress, and if you do it twice in a row, you're just stumped and can't figure out that lock.  Think you're a lock-picking ace?  Get twice the difficulty level of the lock in a single attempt, and you crack it in just one round! 

Same thing goes for disarming a trap.  If you get two 1s in a row, you accidentally set it off.  

How about stealth?  A binary result -- either you're detected or you're not -- is lame.  Instead, if there's someone who could potentially notice you, the GM rolls 2d6 and subtracts your Stealth skill bonus.  Multiply by 5, and that's how close you can get before you'll be noticed.  If the result is zero or negative, you can sneak right up under their noses!  Oh, but the GM won't tell you the number.  You'll never know for sure just how close you can get until you actually try.  Sneaking past a monster at a fair distance is relatively safe and simple.  Skulking right up behind it to take its key ring is lot more daring.

Hear noise (or, more generally, Alertness)?  The GM rolls 2d6 for you and adds your bonus, making it harder for someone to sneak up on you.  If the other guy has Stealth, his bonus is subtracted; the two abilities work against each other.  Listening down a corridor or through a door?  Roll 2d6, add  your bonus, multiply by 5 if through a door or 10 otherwise, and that's how far away you can discern something at the volume of typical speech. 

I haven't yet sorted out how to bring every thief skill into this model, but I'm liking it so far. 

Wednesday, April 20, 2016

Foreshadowing danger

Old school play is associated, for good or ill, with lethality.  Characters can and do die.  Save-or-die is a thing.  Encounter balance is at best a loose guideline, not a sacred entitlement.  Some old school DMs will actually make you roll your hit points at 1st level, and a good many of us don't go in for any of that negative hp business, either: zero hp is dead, full stop.  Some of us don't even allow spells of resurrection in our games.  Dead is dead.  Get out the dice and a fresh character sheet, because your old guy isn't coming back.

That's one of the complaints that new-school gamers have against the OSR: It's a meat grinder.  Who wants to roll up character after character only to watch them die ten minutes after entering the dungeon?  A deadly game and a survivable one don't have to be mutually exclusive, though.  The buffer between fragile characters and the merciless jaws of monsters is player skill.  Old school play is not merely matching character skill against dungeon hazards; it's matching character skill AND player skill against the monsters and traps in the dungeon.  Choices made without information are random, and neither require nor benefit from player skill.  Player skill requires information to make choices -- which means that danger needs to be foreshadowed.

Foreshadowing can be applied to entire dungeons or areas, as well as to specific locations within a dungeon or other adventure locale.  With good foreshadowing, the players can decide to avoid some area if they believe there might be something there they can't handle.  They may also prepare themselves to face whatever is there.

There are lots of ways to go about foreshadowing, and varying degrees of subtlety.  Which ones you use, and how blatantly you apply them depends on the particular situation and the skill level of your players.  Very young or new players will probably need more obvious clues, while long-time players may relish the challenge of a more difficult puzzle. 

Rumors: Before the party even leaves town, they might pick up rumors of very dangerous creatures and places.  Naturally, first-hand accounts are usually the most reliable and least distorted, but tavern tales and folklore have value as well.  If the locals tell you that the Wraith King had every chest in his tomb trapped, or that the orcs have something huge and ravenous chained inside the old mine, or that legend says a demon is sealed beneath the abandoned wizard's tower, you might want to take heed.

Spoor: Direct physical evidence of a creature.  This could be tracks, tooth or claw marks on logs or rocks, droppings, slime trails, shed hair or scales, scorch marks, or whatever signs a monster or group of monsters might leave in its wake or use to mark its territory.

Aftermath of an attack: Bodies, body parts, blood, or equipment and possessions of past victims.  These might bear the marks of how they died for extra clues.  Was it bitten clean in half and left behind?  Bludgeoned to a pulpy mess?  Parts of it eaten?  Robbed or ritualistically disfigured?  All clues for a clever party to interpret.

Behavior of other creatures: Birds, rats, insects, and other creatures may be aware of approaching danger before the PCs are.  Maybe the party's own mounts and animal companions know something they don't.  Do they flee, fall silent, perch all around and watch expectantly, panic, drop dead, chitter or cry warnings to each other, or something else?  What if it's bears, wolves, or elephants flipping out instead of mice and sparrows? 

Smells: Does the monster or its lair have a particular odor? Rotting carrion and brimstone are scents associated with peril, but anything that's different from the rest of the area may be a clue.  Ozone, tar, stale sweat, smoke, acid, mineral spirits, pulverized stone, mold, fresh moist earth ....

Sounds: The chittering of an excited horde of kobolds, the labored breathing of a slumbering dragon, the click of claw on stone, heavy footfalls approaching from far down the corridor, ghostly whispers, howls and roars of rage, the screams of victims or prey ....

Messages: Inscriptions on sealed portals, vague warnings scrawled in chalk or charcoal, a forgotten adventurer's journal, a rat-gnawed map of the dungeon with something illegible scribbled in red, a magic mouth or phantasmal force, hash marks chiseled into the walls beside doors (a secret code) ....

Information from other dungeon dwellers: Maybe the goblins know what lives farther back in the caves, but you won't find out if you just slaughter them on sight.

Sixth sense:  A bad feeling upon entering or approaching some place.  Dreams or premonitions.  Especially appropriate for creatures or places of a supernatural persuasion. 

Changes in the dungeon:  That twenty foot high door made of burnished bronze, when every other door in the dungeon is man-high and made of iron-bound wood ....

Of course, this is in no way intended to be an exhaustive list.  When you describe details which foreshadow danger, it's a good idea to crank your verbal drama dial up a notch or two from your narration of less perilous dungeon features.  A lot of your descriptions are simply background imagery, setting the scene, but foreshadowing is serious business and it's important that you cue your players in to the difference.  Use scary and ominous words.  Repeat yourself if you need to.  Modulate your voice for maximum impact: an awed or sinister whisper, dramatic pauses, or whatever tone you feel best conveys the emotion of the moment.  Leave no doubt in the players' minds that while you've described other rooms in the dungeon as rank and musty, the smell wafting up from that dark staircase is way beyond that. 

For extra impact, double up on foreshadowing.  For instance, the party may hear a story of a knight who bore the token of a sword thrust through an anvil, who was slain by an evil coven of hags.  Then when they find an old rusty shield with the sword and anvil device, they'll know what it means, and what may be in store for them.  Or perhaps they learn of the Wraith King who worshiped a god of unending life and sealed himself away in a vast room full of fabulous treasures, and then come upon a huge golden door deep in a shrine devoted to that god.  Or they discover an adventurer's log with a drawing of a hideous monster accompanied by fevered ramblings of what it did to his companions, and then find granite columns bearing the slashes of huge, terrible claws.

Occasionally, it's OK to throw in a twist.  Maybe things aren't exactly as local rumor has made them out to be.  Perhaps the dragon is really just a gang of bandits stomping around with dragon-foot-shaped boots to discourage anyone from prowling the forest near their hideout, or the giant bellowing dire threats to intruders into the mountains is really just a goblin shouting through a hollow log.  It's important not to do this too often, to reward the players with correct information if they investigate in a way that would reveal the deception, and for it to make sense in hindsight even if they are fooled.

In the end, if your players go charging into a killer encounter and get their party wiped out, it will more than likely be because they chose to take that risk, not because the DM sprang a "Gotcha!" on them that the dice couldn't save them from.

Tuesday, April 19, 2016

From rules-lite dungeon crawl to rules-heavy railroad

Looking back across the years and all the various editions of D&D (and other tabletop RPGs,) you can't help but notice how the hobby has evolved and changed.  Two of the most obvious ways are in the volume of rules and the style of play.  Where once there were unscripted dungeon crawls run with a system described in a rule book hardly thicker than pamphlet-size, now there are carefully scripted and paced adventures geared toward telling specific stories,and rule sets comprising many hundreds of pages spanning two or three volumes or more.

Rules expansions have been driven by a few different factors.  One of the earliest was the need for a uniform set of rules for tournament play.  Beyond that, though, I think once players and GMs master a rule set, there's a natural tendency to explore adding more complexity.  Sure, modeling combat with only attack and damage rolls works, but here's a nifty sub-system for stuns and knockouts, and one for disarming, one for grappling, and one for fighting from horseback.  Here's one to codify exactly what characters' non-class-related skills are and what effects they can achieve.  Here's another to model the effects of fatigue, hunger, thirst, and sleep deprivation on physical and mental performance.  Here's twenty-seven new variant character classes.  And so on, and so forth.

Sometimes these things add interesting choices to the game, which as far as I'm concerned is about the only legitimate reason for rule expansions.  Sometimes they're bolted on in a (misguided, I believe) attempt to increase realism.  In either case, they add complexity, against which the benefits of the new rules are often not adequately weighed.

Players and GMs alike seem to gravitate toward ever-increasing rules-bulk.  Perhaps on some level, the "game" aspect of a role-playing game impelled us to try to fit all the myriad possibilities promised by RPGs into a more familiar game format.  You might house-rule your Monopoly game, for example, but it's still governed by objective rules.  At no time would it be considered appropriate for a player to try something not specifically authorized by the rules, nor for the Banker to make an ad hoc ruling to determine the outcome. 

It's true that within the framework of a rules-lite system, a character can try almost anything, but in a system laden with subsystems, modifiers, and conditional rules, the player doesn't have to rely on the GM's ruling.  These are the odds that the action you want to try will succeed; this is what happens when you succeed, and this is what happens when you fail; it's right there in the book!  The GM is absolved of the responsibility of making rulings which might anger players or provoke arguments: This is what happens, not because I say so, but because it says so right here in the book!

Railroading, at least in my experience, has somewhat different roots.  When I first learned to play the B/X game, I had as my template the module B2: The Keep on the Borderlands, which was an admirable example of a setting without a particular story.  What the PCs did there, and how the inhabitants reacted to them, was the story.  This is true of almost all the early modules for non-"advanced" D&D (i.e. Holmes and Moldvay/Cook.)  Look at the B-series modules up until about B5 or so.  Look at X1: The Isle of Dread.  Even when there's a backstory to the setting, it's meant to provide information to DM and players, and to explain why the setting is currently the way it is, not to dictate an outcome.

Somewhere along the line, though, adventure modules shifted in focus.  Instead of a backdrop against which a game group could generate their own stories, the core of the module was a story crafted by the module's author, and any NPCs and setting elements were there to serve that story, and also unlike those earlier modules, they very likely would never be used or visited again.  These adventures featured programmed, scripted events to drive the plot forward at least as often as they featured map-based encounter keys.  Instead of moving from room to room in a dungeon, the party moves from event to event in a timeline or a set of possible timelines.  While the spatial matrix of the dungeon constrains the absolute freedom of the players to some degree, the narrative matrix of an event-driven adventure limits them in much more profound ways.  Sometimes an adventure seemed to consist of nothing but a series of set-piece encounters, each with the purpose of providing the clue that leads to the next one.  Occasionally, the outcome of an encounter might influence which branch of the matrix the story would proceed upon, but almost invariably the branches converge again at the same climax anyway.  

What drove the change from the spatial structure of the dungeon or wilderness crawl to the temporal/narrative structure of the story-based adventure?  My guess is Frustrated Novelist Syndrome: module authors wanted to show off their storytelling chops rather than just provide game groups with some interesting scenery to chew up in any way they choose.  As reading material, many of these modules are wonderfully engaging.  They're full drama and intrigue, intricate plots set in motion by spectacularly detailed and backstoried antagonists.  There are clues both subtle and explosive weaving every plot thread together, and careful pacing to build tension slowly to a thrilling climax.  And you think to yourself, THIS is what I want my players to experience! 

Perhaps DMs were writing scripted, event-based adventures on their own initiative before the slew of published modules that enshrined the form as an RPG staple, but in my case at least it never occurred to me to do it any other way than the Caves of Chaos/Isle of Dread template until I read some of those magnificent railroads, and I admit that I caught the bug.  

These things represent, to some degree, independent trends in RPG evolution, but they're also connected in some interesting ways.  For instance, an airtight set of rules can facilitate the running of a railroad.  The GM can more easily anticipate what players will do and how often they'll succeed, and players are conditioned not to try anything that's not explicitly endorsed by the rules.  A complex set of tactical rules can also give a player some measure of agency, or at least the illusion of it, when engaging with the various set piece encounters in a railroad adventure.  He may have little or no control over where the story goes between those set pieces.  It may be a foregone conclusion that he and his allies will defeat the ogres blocking the bridge and go on to meet the baron, but with enough flashy character abilities and combat options, he can at least show off his system mastery and beat those ogres with panache!

Both also stem, in large part, from a lack of trust and a corresponding need to exert control.  The players don't trust the DM to make impartial rulings.  The DM doesn't trust his own judgment under pressure.  The DM doesn't trust the players to accept rulings.  The DM or the players or both don't trust in each other to make an exciting, memorable story through spontaneous interactions at the game table.  Ultimately, whatever the merits or demerits of rules-intensive game systems and story-driven adventures, they fail to solve those issues.

What does this say about the OSR, then?  Is there more to it than just nostalgia?  Perhaps a backlash against one or both of these trends, which, while they both clearly have their beginnings in the halcyon days of TSR D&D, are generally scorned by self-identified old schoolers these days? 

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...