Balancing GURPS Combat: Odds to Hit

One of the keys to being a confident GURPS GM is to understand how to create combat encounters that are balanced to the party’s abilities. This post will look at a critical element of combat balance: how likely each side is to land blows. GMs should consider the defensive abilities of the combatants when evaluating how challenging an encounter will be.

Start With Defense

It doesn’t matter how much damage an attack can deal if the blow never lands. Unless the attacker rolls a critical success, the defender gets to attempt a defense roll. As a result, defensive skill is extraordinarily important.

The table below shows the chances of landing a hit based on the effective skills of the attacker and defender. The first thing you should notice is that the attacker’s skill makes a big difference when the defender’s skill is low. However, once the defender’s effective skill gets above 10, most attackers will eek out a hit only one out of three attempts, at best.

Odds to Hit for Effective Attack vs Defense Skills
Odds to Hit for Effective Attack vs Defense Skills

So, when judging how difficult a combat encounter is, the first question should be: how well can each side defend? If the player characters are facing an opponent that has a base active defense skill above 10, they need to have ways to lower the effective defense skill in order to expect to land blows with any regularity. Conversely, if the players have a high active defense skill, the opponents should have ways to lower the effective skill in order to put the characters into jeopardy.

When Defense Isn’t Enough

Defense skills are important for balancing combat, but there are some situations in which even the best defensive skills aren’t enough:

  • Lethal damage: if an attack can do lethal damage with a single blow, then a high defense skill doesn’t eliminate the risk—it just makes the outcome a high-stakes gamble. A single good (or bad) dice roll can radically change the result, so the GM needs to be prepared to handle the worst.
  • Area effects: when an attack targets a large area, there may be no active defense possible. Area effects may give PCs a way to take down NPCs with extremely high active defense skills, but opponents can also use these effects to circumvent player defenses.
  • Mental attacks: Physical defenses are useless against mental assaults. If a character can terrify an opponent, manipulate their senses, or otherwise get inside their antagonist’s head, the GM should think about how that will play out in combat.
  • Surprise attacks: Finally, active defenses are useless if the target never sees the attack coming. The players (or NPCs) can make tactical decisions to give themselves the element of surprise during the combat, but the GM should also think about whether one side can set up an ambush before the battle is joined.

Faster Combat by Pre-Rolling Dice

Dice in cigar boxGURPS combat uses a lot of dice rolls. In addition to attacks and damage rolls, GURPS uses rolls for active defenses, skill checks to handle difficult terrain or maintain concentration, and even morale checks to determine if enemies will flee.

Good GMs know that it is important to keep combat moving in order to maintain player engagement. One way to maintain the focus on the player’s decisions is to streamline NPC time. With all the dice rolls in combat, one easy way to spend less time resolving NPC actions is to pre-roll the dice for NPCs.

Rolling in Advance

When players roll the dice, it’s exciting! They want to find out the result of their actions. Every roleplayer will have memories of phenomenal rolls that snatched victory from the jaws of defeat—or embarrassing recollections of a truly unlucky roll at the worst possible moment.

Waiting for NPCs to resolve their actions is less interesting. The players want to know what happened, but the suspense of figuring out the dice roll is far less engaging. And, if the players spend too much time waiting for NPCs to finish, they become bored.

While rolling and adding up dice can be time-consuming in game, there’s no reason that the GM has to spend that time during the game. The GM can instead pre-generate a sequence of dice rolls and simply refer to that list during the game.

How to Pre-Roll

The easiest way to generate a list of dice rolls is to use a digital dice roller and record the results in the order they were rolled. Because all success rolls in GURPS use 3d6, the GM can create a list of 3d6 roll results. Then, whenever the GM needs a success roll for an NPC, he or she can look up the next result on the list, use that number, and cross it off. As long as the dice roller is random, there’s no functional difference between rolling in the moment and using the very next entry in a pre-generated list.

There’s one caveat: the GM can’t look at the number before deciding what the NPC will do! The NPC doesn’t have foreknowledge and so the GM shouldn’t be able to strategically choose the skill or modifiers in order to ensure a success (or failure). The GM needs to choose the action, determine the effective skill level, and only then look at the list. The GM also has to take the very next number; it’s no fair skipping around to avoid a critical hit or miss!

This technique can be expanded for other common rolls. For instance, if many NPCs will be making 2d damage rolls, the GM can generate a separate list of 2d results. However, the biggest payoff comes from the 3d6 list because the vast majority of GURPS rolls use 3d6.

Creating Pre-Rolled Lists in Excel

excel-preroll
List of pre-rolled 3d6 results in Microsoft Excel

If you have Microsoft Excel, you can easily create lists of pre-rolled dice results. Other spreadsheet programs will have similar functions, but you may need to adjust the formula to match the program’s function names.

In Excel, create a new spreadsheet and select a blank cell. Then, use Excel’s built-in random number generator to roll three dice by copying and pasting the the following formula:

=RANDBETWEEN(1,6)+RANDBETWEEN(1,6)+RANDBETWEEN(1,6)

The RANDBETWEEN function generates a random number between the two bounding numbers, so RANDBETWEEN(1,6) is equivalent to rolling a single d6. Since we want to roll 3d6, we use that formula three times and add them together.

From there, we can copy and paste that formula into additional cells until we have enough results. Note that each time you change a cell (including pasting this formula into a new cell), Excel will recalculate all the formulas in the spreadsheet. So, you’ll see the numbers change as long as you are building the sheet. That’s fine. Just print out the spreadsheet when you’re done, and use those numbers.

If you want to roll a different set of dice, you can do so by changing the formula. If you decide to roll damage, remember that GURPS does not allow damage to go below 1 (for crushing damage, below 0). You can use the MAX function to impose a lower bound on the result. For example, to calculate 1d-3 piercing damage, you can use the formula below:

=MAX(1,RANDBETWEEN(1,6)-3)

Ballparking Damage in GURPS

In the heat of combat, the last thing you want to do is pause to look up a a rule. GURPS has detailed weapon statistics that players can write on their character sheets before the game, but sometimes the GM needs to improvise. The PCs accidentally alerted the night watch and you need a polearm’s damage? A character turns a length of rope into a makeshift lasso? When the GM needs to come up with damage numbers on the fly, it can be helpful to make a ballpark estimate of how much damage an attack should generate.

This post provides order-of-magnitude estimates for how much damage weapons do. This is a deliberate oversimplification meant to give GMs guidance when figuring out reasonable estimates: it rounds numbers from the Basic Set, skips over rules in supplement volumes, and doesn’t look at special kinds of damage like armor divisors, fragmentation, and cyclic damage. Using this scale, GMs can choose damage rolls that pass the eyeball test.

Damage Roll Estimates

1d-3: Attacks that deal this level of damage are minor. When relevant, any kind of armor can absorb this magnitude of damage. Any injury that gets through won’t have much effect unless the character is damaged repeatedly.

  • Bite (average strength)
  • Fire (momentary exposure)
  • Poison (mild)
  • Punch (average strength)

1d-2: This category is a little more dangerous. Weak armor may not absorb all the damage, but the injury isn’t usually severe on its own.

  • Bite (above-average strength)
  • Kick (average strength)
  • Punch (above-average strength)

1d-1: This level of damage starts to leave an impact. A high roll can take out nearly half of a character’s HP without protection, and multiple hits will quickly accumulate the injury even under the best of circumstances.

  • Bow (average strength)
  • Fire (sustained exposure)
  • Kick (above-average strength)
  • Knife (average strength)

1d: Attacks at this level can knock out a normal, unarmored human in two hits! Even a single hit can cripple a limb or cause major injury.

  • Bite (extraordinary strength)
  • Bow (above-average strength)
  • Knife (above-average strength)
  • Longbow (average strength)
  • Poison (strong, e.g. arsenic)
  • Punch (extraordinary strength)

1d+1: Armor is almost mandatory to withstand these attacks. Unprotected characters can expect to lose limbs or collapse from shock.

  • Axe (average strength)
  • Bow (extraordinary strength)
  • Crossbow (average strength)
  • Kick (above-average strength)
  • Longbow (above-average strength)
  • Spear (average strength)
  • Sword (average strength)

2d: These attacks can fell an unprotected human in a single blow, and even armored characters will be in trouble if they suffer multiple attacks!

  • Axe (above-average strength)
  • Crossbow (above-average strength)
  • Knife (extraordinary strength)
  • Longbow (extraordinary strength)
  • Poison (severe, e.g. cobra venom)
  • Quarterstaff (average strength)
  • Spear (extraordinary strength)
  • Sword (above-average strength)

3d: At this level, even basic armor may not be enough to keep a character alive. Unarmored characters will need a great deal of luck to withstand an attack and continue functioning.

  • Axe (extraordinary strength)
  • Crossbow (extraordinary strength)
  • Flamethrower
  • Grenade (powder)
  • Machine gun
  • Quarterstaff (extraordinary strength)
  • Revolver

4d: Unless you are extraordinarily well protected and lucky, your character is out of the battle once one of these blows lands.

  • Grenade (fragmentation)
  • Laser weapon
  • Poison (deadly, e.g. cyanide)
  • Rifle

Beyond 4d: Attacks that do more than 4d damage tend to be either superscience weapons, futuristic technology, or weapons designed for heavy targets rather than attacking individuals. You can scale the numbers as large as needed, but it may make more sense to give the weapon an armor divisor or affliction rather than just increasing the numbers.

Notes

In the examples above, “average,” “above average,” and “extraordinary” refer to the human norm (specifically ST levels of 10, 12, and 15). It’s not uncommon for realistic animals to reach ST levels of 20, and of course fictional creatures can have far higher strength levels. In those cases, extrapolate as necessary!

The damage rolls were chosen based on the GURPS logarithmic progression. GURPS uses a six step progression in several places, most notably the Size/Speed/Range table, to scale modifiers among several orders of magnitude. The progression goes: 1, 1.5, 2, 3, 5, 7, 10, and then repeats with the new order of magnitude as the base level (so 10*1.5 = 15, 10*2 = 20, etc.). The damage rolls listed yield an average damage that roughly tracks this progression.

Aborting Combat in GURPS

Balancing combat in GURPS can be challenging, especially for new GMs. Running combat encounters is much easier when the GM knows how to abort a battle that is overwhelming the player characters.

Sometimes, the players deliberately bite off more than they can chew; in those cases, it makes sense for the battle to carry a lot of risk, and the GM is justified in letting the players suffer the total party kill that they have brought upon themselves. But most of the time, TPKs emerge by accident; the GM miscalculates what the PCs can handle, and the resulting carnage is a serious disappointment. GMs therefore want to minimize the risk of accidentally annihilating the party.

There are some obvious ways to bail from combat if an encounter is too deadly: having the NPCs suddenly pull their punches, adjusting stats on the fly, or fudging dice rolls. However, these actions can leave both the GM and players feeling cheated. It’s nice to avoid a total party kill, but it’s better to not put the players into that situation in the first place.

Fortunately, there are also ways to escape from combat situations that don’t undermine the narrative of the game. This post will discuss some of those techniques for GMs to end the combat without breaking the game’s immersion.

Negotiating a Cease Fire

Not every combat needs to continue until one side dies or passes out. One side may recognize that the other side wants something other than their death, and can offer to negotiate in exchange for safety. Or, the participants may be governed by a code of conduct (or legal norms) that accord privileges to those wishing to negotiate a stand-down.

Jack Sparrow invoking the right of parlay
Jack Sparrow invoking the right of parlay

In Pirates of the Carribbean, Jack Sparrow is captured at gunpoint when he remembers that the pirate code entitles him to parlay. He invokes his right to negotiate with the captain and is guaranteed safety until the negotiations are concluded. Jack is not out of the woods—and in fact his negotiations do not end well—but he averts his nearly certainty death at the hands of the crew.

The GM should make sure that his or her players know negotiated surrender is an option. But, the GM can also take the initiative in calling for negotiations. When the NPCs are firmly in control, negotiating for their goal is less risky than chancing a lucky shot from the PCs. As a result, the NPCs may have an incentive to de-escalate the situation and make the PCs bear the burden of their loss in the terms of surrender.

To set up a negotiated settlement, the GM should think through what motivates the NPCs. If the NPCs are simply cannon fodder for adventurers, then negotiation isn’t likely. However, if the NPCs have their own goals, pressures, and responsibilities, then there is room to negotiate a solution that moves the NPCs closer to their objectives.

Changing the Environment

Most new GMs think about the combat environment as a constant: once the space is set up, the characters make the action happen. But, the environment doesn’t have to be fixed. A power outage can cause the lights to go out, letting some characters escape, or the ledge suspended over a chasm can crack, threatening the safety of the characters standing there. Even something as simple as the passage of time can have an effect: when the sun rises, undead may have to retreat to the shadows.

If the PCs are truly overwhelmed, the GM can strategically change the environment to give them the initiative or provide a route for escape.

Changing the environment works best when the GM doesn’t save it for emergencies only. If the GM only changes the environment when the PCs are up against the wall, it feels like a cop-out. But, the GM can make environmental changes regular parts of the combat experience. Mist and smoke can obscure the battlefield as combat goes on; the walls can start to crack from the force of repeated impacts. Rivers can flood, fires can spread, reinforcements and allies can show up, and mana levels can ebb and flow. Having the environment change every round or two of combat makes battles feel more dynamic.

A savvy GM will mix up the impact of environmental changes. If the environment always benefits the players, it feels gimmicky. But if the changes sometimes benefit the opposition, they makes combat feel more uncertain and tense. Some environmental changes can be neutral, forcing both parties to adapt their tactics; others can be curve balls that change the whole dynamic of the encounter.

The GM can also gain credibility when changing the environment by linking environment changes to combat events. A boulder is unlikely to appear out of nowhere and cut off the pursuers—but if the characters were setting off explosives, suddenly the resulting avalanche is a creative effect of their actions.

Shifting the Threat

When one threat is poised to wipe out the party, the GM can breathe life into the encounter by shifting the threat to an even greater danger.

Fellowship of the Ring surrounded by goblins
Fellowship of the Ring surrounded by goblins

In The Fellowship of the Ring, the party seems doomed when they are surrounded by goblins deep in the mines of Moria. But, when the goblins hear a noise from the depths, they run away in a blind panic and leave the party to their own devices. Why? Because it turns out that goblins are not the worst thing in the dungeon—not by a long shot. The dungeon is also inhabited by a Balrog, a demon that so outclasses the goblins that they will flee for their lives even in the face of overwhelming victory against the party. With the goblins dispersing, Gandalf is free to lead the group on a wild race to escape the Balrog and find safety.

This trope of shifting the threat occurs in many works. For instance, in Jurassic Park, the protagonists are trapped by velociraptors in the Visitor Center, and they seem doomed until a T-rex breaks in and takes out the raptors. A variation of this trick occurs in Star Wars IV: A New Hope; the Tuscan Raiders that have captured Luke are scared away by the sound of a desert creature (that turns out to be a ruse played by Obi-Wan Kenobi).

Shifting the threat is a little bit of a deus ex machinca, so it needs to be used with care. It works best when the now-vulnerable antagonists have reason to think that the new threat is more dangerous, and it keeps the tension high if the PCs face greater risk as well. Note that the risk doesn’t have to be the same: the Balrog is threatening as a magical creature, while the goblins simply posed a mundane threat. What matters is that the stakes feel raised.

A little bit of foreshadowing can also improve how shifting the threat is received. The tyrannosaur is set up as a dangerous predatory early in Jurassic Park, so the T-rex’s attack doesn’t come out of nowhere.

To prepare the game for a possible shift in threat, the GM can think about who or what else is involved in the game world. Are there mutual opponents that can intrude? Do the antagonists have their own rivals that may interfere? Setting up these kinds of interconnected plot lines also makes the world feel three-dimensional, which enhances the atmosphere of the game.

Playing into Overconfidence

Finally, the antagonists do not need to go for the killing blow right away. Villains are frequently victims of their own hubris. They stop to gloat, to share their plans for inevitable victory, and to force the protagonists to watch their triumph.

If it fits with the personality of the NPCs, this option can be used to end a combat scene without a TPK. The player characters can be surrounded and lectured by the antagonist, who accidentally reveals a secret that the PCs can exploit. Or, the PCs may simply have enough time to catch their breath, recover a fatigue point, and overwhelm the opposition with a surprise all-out blitz.

Antagonists will frequently choose to capture the main characters and lock them away rather than killing them outright. GMs can easily use that option in order to end the combat and steer the campaign into a jail break scene. Depending on the genre of the game, it may be appropriate to include an interrogation session or an attempt to torture the PCs for further information; in other genres, the PCs may discover additional captives that can be allies in their escape attempt. Sometimes, the PCs may be able to bribe a guard to help them sneak away; other times, the captors are simply inattentive or overlook crucial details. Any of these options creates interesting possibilities for the game to advance.

Summary: Keep the Story Going

These four techniques to abort a combat scene all give GMs the ability to adjust on the fly if an encounter is too challenging for the PCs. The important thing is that all of these methods keep the story going. By adding twists to the situation, the GM can make the story more compelling. Having these techniques in your back pocket is a far better solution than simply fudging die rolls.

Understanding Damage in GURPS Combat

GURPS has a reputation for lethal combat, which catches many new players by surprise. This reputation stems from a different conceptual model of damage. When you understand what damage means in GURPS, it becomes easier to know how to enjoy combat—or how to adopt optional rules in order to create the experience you do want.

Many RPGs treat hit points as a reserve that is intended to be used. Your character’s hit points gradually wear down in combat, like ablative armor, and that’s okay if you can wear your opponent down to zero first. As long as you stay above zero (or a specific “bloodied” threshold), there’s no difference between being fully healthy and just hanging on. As a result, characters can take a beating and keep on dishing it out, and in fact it is expected that your character will take lots of damage during combat.

By contrast, the default assumption in GURPS is that damage hurts. When your character gets injured, he or she is less able to function. As a result, even a single point of damage can influence future rounds of combat, and those effects can stack up over time.

The cumulative effect of taking any damage is sometimes referred to as the GURPS Death Spiral. A single injury causes a shock penalty, which makes it more likely that the character will be hit the next turn, which makes it more likely that the character will cross the 1/3 HP threshold and slow down, etc. Consequently, avoiding injury is more important in GURPS, and if you get hit you need to adjust your tactics rather than barreling through the pain. In short, it’s usually not a good strategy to just assume that you can dish it out faster than your opponent.

Implications of the “Damage Hurts” Model

Because GURPS assumes by default that damage hurts, combat plays out a little differently than in other systems.

  • Going first matters: Being able to strike the first blow gives your character a huge advantage. GURPS emphasizes the importance of speed by having characters act in combat in order of speed, rather than rolling for initiative. So, you can control how quickly you act more than in other systems—and you should use that to your advantage.
  • Avoiding damage is crucial: GURPS encourages players to avoid damage through the strategic use of cover, terrain, dodging, or blocking. If your opponent can’t hit you, they can’t hurt you. It’s rare for a GURPS battle to be a bashing contest; the players have a strong incentive to choose better tactical approaches.
  • Armor keeps you alive: When you do get hit, it’s important to limit how much damage your character takes. Without good armor, a single bullet can down a character.
  • Healing during combat is less relevant: It’s possible to heal characters during combat, but it’s not as common as in other games. Because the act of taking damage matters much more than how many hit points a character has left, healing is less valuable than avoiding damage in the first place. Characters that can buff their party members by improving their defenses, armor, or the like give their party a massive advantage.
  • Not fighting is a compelling option: Because a single lucky shot can down a character, players have an incentive to find alternatives to combat (or to push for surrender rather than waging battle to the final kill). To be clear: GURPS is fully capable of giving you a knock down and drag out fight. But, as a player, there are advantages to wrapping up the fight quickly.

Changing GURPS’ Assumptions

The “damage matters” model is the default in GURPS, but it’s very possible to run GURPS through the “hit points as reserve” model. By turning off a number of the combat rules and/or equipping your player characters with specific advantages, you can create the effect of other RPG systems.

  • Eliminate shock penalties: Shock penalties make damage matter from the very first blow; a character that is injured has a penalty to all their rolls in their subsequent turn. The GM can ignore the shock rules, or the PCs can take the High Pain Threshold advantage.
  • Turn off realistic combat rules: Major Wounds, Knockdown, Crippling Injury, and Mortal Wounds are all inconsistent with the “hit points as reserve” model. The same goes for the optional rules of Bleeding and Accumulated Wounds. Turn off all those rules, and damage starts to function closer to the reserve model.
  • Ignore hit locations: Hit locations can make combat extremely lethal because they allow characters to target around their opponent’s armor and to get substantial wounding modifiers. You can still play the hit points as reserve model with hit locations, but it requires an additional level of tactical awareness for your players.
  • Ignore wounding modifiers: Wounding modifiers also make combat far more lethal; cutting, impaling, and large piercing attacks in particular become much stronger when wounding modifiers are in play. Since those modifiers include common kinds of attacks like swinging a sword, stabbing with a lance, or shooting a gun, wounding modifiers can cause characters to run through hit points quickly. Again, it’s possible to play the hit points as reserve model with wounding modifiers, but your players need to be prepared.
  • Restrict HT checks: The default rules have characters making HT checks when they drop to zero HP, and then at each negative multiple of HP until the character dies at -5xHP. These rules make additional degrees of damage more severe, so the GM should limit these checks in order to approximate the hit points as reserve model. The advantages Hard to Kill and Hard to Subdue give PCs a bonus on those checks, mitigating the impact; alternatively, the GM can choose to simply ignore these checks.