Monday, November 29, 2021

The Effect of Sweep Attacks

Conan the Destroyer

For quite some time, it's been left as ambiguous in my OED House Rules whether or not fighters get "sweep" attacks -- the hyper-accelerated mode where they take as many attacks per round as they have levels, but only against low-level (1 hit die) creatures.

One of the major themes for this year, both on my blog here (and here) and in discussions on the Wandering DMs YouTube channel, is my finally becoming convinced that (a) that rule really was intended consistently throughout Gygax's Chainmail, OD&D, and AD&D, (b) it's a critical aspect to balancing against the large mobs of 1-HD humanoids who appear in groups of hundreds, and (c) it's the single biggest rules difference between the O/AD&D lines and the Basic D&D lines (where the rule is removed, and humanoid numbers greatly reduced). 

So granted that, I think I need to make an explicit call about whether that's a base assumption for OED, and in my next update, in line with the classic game, I'll be highlighting that as an included rule. (And also removing "cleave" from the list of optional feats, but then I never saw a player pick that anyway, so it's a minor issue.) 

In some ways it's actually not my favorite rule; I'm less than thrilled with the discontinuity between 1 and 2 HD, and the possibility of a large number of dice being rolled. But the advantages of recognizing it include: (a) closer compatibility with the original game, (b) recreation of inspirational pulp stories (where heroes like Conan indeed hold off huge mobs), (c) some way for fighters to hold pace with high-level wizards, (d) less modification needed vs. reducing all the humanoid numbers appearing, and (e) a mechanic that legitimately makes high-level fighters significant in mass combat, such as Book of War

(And I'm less bothered by the OD&D FAQ/Swords & Spells presentation of, "base 1 hit die or less", versus the AD&D version of strictly "less than one hit die", which made the switchover difference a single hit point, e.g., leaving goblins in but taking orcs out.)

If a DM looks at OED and wants to snip out the sweep attack rule (and commit to changing monster numbers appearing), then that's fine and respectable -- and I think easier than if I left it out and another DM needed to add it back to the system. There were some other alternatives that I considered and tested along the way (like a generalized "cleave" rule, or changing every single monster number in the game), but I wound up rejecting those, so I won't go into them here.

Here are some other observations on the effect of sweep attacks, based on recent investigations.

Arena Simulator

Recently I modified the code in the Arena Simulator on Github to add an optional switch to turn on sweep attacks (-w). What we see is that on average, the power value of the 1-HD monster types gets cut down to about one-quarter basis. This is summarized in the following table; here, EHD is "Equivalent Hit Dice"; the average number of fighter-class hit dice the monster can evenly match up against.

Sweep Metrics Compiled

Normally the EHD calculation seems fairly robust to me, because it's an average over what I call the EFHD value (Equivalent Fighter Hit Dice) at each fighter level, and that latter number tends to be roughly constant over different levels for standard monster types (at least within a factor of about 2 or so). Some exceptions stand out for monsters with big area attacks or high hit-by magic (kill lots of low-level fighters, generating a right-skewed EFHD distribution), or ones with potent save-or-die effects (more easily wipe out high-level fighters' hit dice, giving a left-skewed EFHD distribution). 

And now, monsters subject to sweep attacks present another outlier case, because the lethality of the fighter-types suddenly varies so much by level, due to their many-multiplied attacks. (Normally fighter stamina is increasing by level, while attacks stay about the same; in this case fighters become quadratic, too.)

So let's look at that a little more closely. The interesting thing is that sweep attacks actually change the EFHD curve slope from positive to negative. For example, here's a listing of the EFHD values for an orc, matched against fighter levels 1 to 12, with sweep attacks on, from the Arena simulator (-e and -w switches):

[1.0, 0.67, 0.6, 0.5, 0.42, 0.35, 0.29, 0.25, 0.2, 0.18, 0.16, 0.14]

As expected, the value of the orc decreases from EFHD 1.0 at 1st level (indicating that a 1st level fighter can hold off 1 orc), to EFHD 0.14 at 12th level (indicating that a 12th level fighter can fight off about 12 / 0.14 = 85 orcs). Now, what might be more surprising is the EFHD curve for an orc before the sweep attacks get turned on as shown here (using just the -e switch):

[0.5, 1.0, 1.0, 1.0, 1.0, 1.2, 1.17, 1.14, 1.13, 1.25, 1.22, 1.2]

What that shows is that the pro-rated strength of an orc (or other basic monster type) is normally increasing somewhat versus fighter level; e,g., from 1.0 at 2nd level to 1.25 at 10th level or so. It may be easy to overlook, but that's not really a mystery: we've long identified that as the effect of the Packing Problem, in that mobs of low-hit creatures are effectively sponging up more wasted overkill damage, whereas high-hit figures are suffering full damage from every hit but the last.

The effect of sweeping is so powerful that I had to increase the MAX_ENEMIES cap in the simulator from the previous 64 to 256. (E.g.: a single sweeping 12th-level fighter can hold his own against some 80 orcs as above, 160 kobolds, or 240 rats). This had a side effect for certain powerful monsters that are only hit by higher-powered magic items, like elementals (+2 to hit) and golems (+2 for stone, +3 for iron). Granted that no low-level fighters can possibly have such magic weapons in the simulator, those monsters effectively stomp an infinite number of normal men. And when the MAX_ENEMIES number goes up, then their computed EHD goes up. So that will be reflected in the next OED Monster Database update. Iron Golems are now assessed at EHD 125!

On the other hand, I don't intend to change the EHDs listed for the 1-HD types (mostly EHD 1), because: (a) I don't want to deal with fractions there, (b) I don't want to trick anyone into throwing 4 orcs at every 1st-level fighter, (c) as noted, the averaging process is a bit cracked in this outlier case, and (d) maybe some DMs won't be using sweep attacks in the first place.

Experience Awards

Classic versions of the O/AD&D game generally have a rule for pro-rating experience in the downward direction; that is, awarding only a fraction of the experience based on monster or dungeon level divided by character level. (E.g., from OD&D Vol-1, p. 18: "Gains in experience points will be relative; thus an 8th level Magic-User operating on the 5th dungeon level would be awarded 5/8 experience."). Personally, I hate this rule, most people I know ignore it, it creates unsolved problems with multi-character parties at different levels, etc. 

Generally speaking, I don't think that rule makes any sense when the XP leveling tables are already themselves designed on a geometrically-increasing basis. Assuming we think of XP awards as generally balanced to the danger of the encounter, as noted above, we find that EFHD values are usually about constant across levels -- or in other words, danger is really linear in standard hit dice. The takeaway is that XP as a constant multiplier by HD (say 100 points per HD), and without taking a ratio for PC levels, is not a ridiculous thing to do.

But in the particular case of sweep attacks, that's certainly not true; the relative danger levels posed by goblins and orcs in the face of Superhero Cuisinart attacks indeed drop like so many carrot peelings. So for the first time ever, I could see the twinkling of an argument for reduced XP by a ratio of levels -- if one were focused specifically on the Hero-vs-mooks case as a default D&D fight, then the ratio-reduction is in fact legitimate. 

I still don't think I'll use that rule in the general case, but I could start to imagine engaging it, specifically in the unique case of PCs versus armies of 1-HD humanoids who are getting mowed down for pulp narrative purposes.

And we're not quite done with the issue yet: next time, we'll revisit the OD&D wilderness encounter tables in the context of the sweep attack mechanic.

Do you use sweep attacks in your OD&D-flavored games? Or if not, do you drastically reduce the humanoid numbers appearing? And do you use the XP ratio-reduction rule, maybe just in this one special case?

31 comments:

  1. I use sweep attack in my Swords & Wizardry game. It came up yesterday. The party was fighting a large group of little humanoids about 18" tall. They have AC10, 1 HP, and do 1d2 damage. There were 100 of them. The party was a 5th level cleric, a 3rd level fighter, a 2nd level fighter henchman, and 4 other humanoid hirelings that were 3rd level fighter equivalent but with d10 HD rather than d8 HD.

    The monsters swarm attack and being so small, they surround and try to bear down the targets. Each character is getting as many as 10 attacks at a time. I rule that if you get hit with 5 successful attacks, you have to make a roll under Str check to avoid being brought to the the ground where you can't attack and have to make another Str check to stand up again. If a character goes under 0 and gets brought down, the creatures fighting that character continue to gorge themselves on the character and ignore the combat for 1d6 round.

    The party baited them into a pit trap and killed 20. They had done this from range and picked off another 10 or so with missile fire before they got to melee. We lost two hirelings, the cleric was down to 4 HP, the fighter was getting low. It took quite a while for them to defeat the horde, 20 rounds maybe? I didn't keep track.

    They managed to kill as many as 10 a round but averaged about six. The players were getting kind of nervous. They won but it was closer than they liked.

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    1. Sounds exciting! That's definitely the kind of big action I want to see in my games, too.

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  2. I use Classic D&D (BECMI specifically) as my base rules, but brought in Sweep from OD&D. So far, it has been a big boost to the fighter types, but since the highest level PC is 7th, we haven't seen it as overpowered yet. It definitely speeds up melees with many low HD opponents, and the magic-users are often saving their fireballs and lightning bolts for dealing big damage to stronger monsters, rather than using them for crowd control.

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    1. Very cool! I was wondering how many people ported it in in that direction. (You'll see in a linked item above that Frank Mentzer himself is explicitly against the rule.)

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  3. I'm not sure, but I think that I read that rule as the fighter getting a bunch of attacks equal to his level, but that each attack was an attack as a level 1 fighter. Perhaps this is reflected in the AC values of the monsters that such attacks apply to. Perhaps I'm reading the rules wrong.

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    1. This is a big issue for me. How to handle all bonuses when sweeping, both to-hit and damage. I'm thinking maybe divide bonuses by the number of foes...

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    2. That's another key detail, that I didn't get into here. Maybe I should have. It's absolutely a fair reading of the passage in OD&D Vol-2, p. 5 (explicitly just for monsters, and translating the "as a man-type" from Chainmail-speak). On the other hand, that restriction is definitely not in AD&D (so, another point of bifurcation).

      I've never seen anyone play that way, but seem people on the ODD74 forum claim to do so. For my game, I don't think I want to tell a player some different base attack bonus to recompute.

      Although if I did, my preference would just be a null attack bonus, i.e., roll some raw d20s and tell me what shows up, no math.

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    3. ... also it should be noted that all of the places where Gygax is explicit about PC fighters getting sweeps are also explicit that they get their full attack chances, not at 1st level. D&D FAQ in TSR #2, and Swords & Spells are very clear that a hero will be rolling on the 4th level table for their multiplied attacks vs. orcs.

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  4. Also, I don't know if there's anything in the rule that states that the attack has to be melee, which, if true, is hilarious.

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    1. That seems pretty clearly stated in multiple places, e.g.:

      OD&D FAQ (TSR #2, p. 3): "... this is treated as normal (non-fantastic) melee, as is any combat where the score of one side is a base 1 hit die or less."

      Swords & Spells p. 1: ".... (or orcs or similar 1 hit die creatures), an actual melee can take place..."

      AD&D PHB p. 25: "This excludes melee combat with monsters (q.v.) of less than one hit die..."

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  5. The other thing that confuses me about sweep attacks is how much movement is involved.

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    1. Yeah, it's true this implies at least some kind of abstracted movement in the melee (esp. for very high levels where there's more attacks than creatures adjacent in an instant).

      On the other hand, I'm told the AD&D Gold Box video games did limit sweep attacks (where we get the term, in fact) to stuff immediately adjacent on a fighter's round.

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    2. When it comes to abstracted movement in this case, I think the best mechanism is to make combat rounds 1 minute abstracted, as per 2e. :(

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    3. Actually, even disregarding movement, attacking 10+ people in 5 seconds is nigh impossible. :)

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    4. Separate attacks, I basically agree. When I need to visualize it, I go towards the idea of single sword-strokes going through multiple bodies. (And that's why I tend to think "cleave" is the best term for it.)

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  6. I've just always included the fighter's Heroic Fray ability as a matter of course in my campaigns, though I also expand on it and simplify its operation (as I've mentioned in the comments on other posts).

    Instead of rolling to hit once per level, I find it much quicker (and barring outlier armor classes, the results aren't much different) for the fighter to automatically kill 1d[level] mooks within reach per round. (When the party is outdoors, and large mobs of humanoids are imminent, the fighter who brought along a 15' pike is a really happy guy.)

    But as to the HD of enemies affected, that varies a bit with the system in question. If I'm running a traditional game of D&D (any edition), I'll explicitly state that fighters can affect less-than-1 HD enemies starting at 4th level (Hero), 1 HD enemies at 8th level (Superhero); and then, for very high-level fighters, enemies with 1/10th the fighter's level in hit dice are affected (so 1+ HD starting at 15th level, 2 HD at 20th level, 2+ HD after 25th level, 3 HD after 30th level which is the maximum possible in AD&D, and then 3+ HD after 35th level in D&D). But for foes with >1 HD, the number the fighter rolls is divided by the enemy hit dice to find the number of monsters killed, so that (e.g.) if a 16th level fighter is sweeping hobgoblins, the procedure is to roll 1d16 and divide by 1½ to get the number of hobgoblins killed each round.

    An alternative that I've used sometimes (and this works for me because I tend to fix enemy hp rather than roll them, so that all ½ HD monsters always have 2 hp, all ¾ or 1−1 HD monsters always have 3 hp, all 1 HD monsters always have 4 hp, all 1+1 HD monsters always have 5 hp, etc.) is that a fighter can Fray any monsters (or characters!) that have hp ≤ ½ the fighter's level. In practice, this means that a 4th level fighter can slay 1d4 enemies of ½ HD per round, a 6th level fighter can slay 1d6 1–1 HD enemies per round, an 8th level fighter can slay 1d8 1 HD enemies per round, etc. (I only use this method in systems that don't scale levels much above 10th.)

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    1. Very interesting, thanks for that! It was just in the last month or two I heard about Gary and/or Dave rolling a single 1d8 for number killed by a Superhero (e.g., etc.). I must say that extremely attractive.

      But at the moment I think I'm prone to roll a batch of d20s -- or even convert to d6 targets -- and probably call any hit a kill.

      It's interesting the ways people vary that rule, but for compatibility & simplicity sake at the moment I am sticking with the OD&D FAQ/Swords & Spells rule that it's simply for 1 base hit die types.

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  7. IIRC, OD&D XP wasn't geometric, it was a flat 100 xp per HD, no? Or am I misremembering?

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    1. In the LBBs, (Vol-1), that's definitely what it says. As of the OD&D Greyhawk supplement 8 months later, Gary wrote that was "ridiculous" (p. 12) and presented the quadratic awards for the low end that appear from then in in B/X, AD&D, etc.

      Previously I've called that Big Switch and the Khopesh Curve.

      As noted above, I'm really a much bigger fan of that original flat 100 per HD award (esp. in the face of the geometric class advancement tables).

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  8. I know you decided against a general cleave attack, but allowing a free attack after dropping a foe, along with escalating damage bonuses for fighters, goes a long way towards long term balance. Fighters get a max number of attacks up to their level. Clerics and thieves up to half their level.

    Against low level foes, they drop like flies and makes fighting masses possible. Against higher level foes it can speed up combats. I also give it to monsters, but high HD PCs generally aren't effected (but henchmen are).

    I allow movement between cleaves up to max movement in a round, but make the person make a save vs paralysis to move after the 2nd cleave to avoid slipping or falling over bodies, entrails, etc. if it is a cluttered battlefield. Going through the G1-3 modules with this mechanic made some of the pitched battles a blast.

    I also have a critical hit rule allow an critical if a to hit roll exceeds its number by a specified amount by class (generally 10 over for fighters) which increases average damage to about 17 for an 8th level fighter, making mass combats against ogres and giants possible.

    Not for everyone, but it makes the PCs feel like hero's, and skilled monsters scary in melee.

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    1. I'm very sympathetic to that! Obviously I had the cleaving at least as an option in my house rules for fully 10 years, and it was kind of painful for me to remove it.

      Among the things that put me over the edge was (a) becoming convinced that the sweep-attacks rule was a consistent intent through the Chainmail, OD&D, and AD&D sequence, and (b) the advantage that with sweep attacks, you know the number of attacks up front and can roll one big batch of dice (as opposed to cleaving which is conditional, so you have to roll, check, roll, check, etc. which can take longer, and I've seen it pose ongoing confusion to a new convention player).

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    2. The ability to roll multiple dice at once is actually something I hadn't considered. That makes a lot of sense.

      BTW, whenever I have masses of enemies, I just assume average rolls and apply them, so instead of rolling 20 attacks, I assume I roll each result. This was so effective last time I used it, I might apply in in groups of 10 going forward.

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    3. Yeah, that also makes a lot of sense. I've even warmed up to things like (a) make one roll and apply to all attacks, (b) just roll a d8 for a superhero and declare that many kills.

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  9. How does sweeping actually work when fighting several foes with differing HD (e.g. when surrounded by three orcs and a bugbear)?

    Is sweeping done instead or on top of the regular attack? If it's the latter, could the regular attack be directed at a foe already targeted by sweeping?

    I understand the 1 HD demarcation, but are there other ideas (like John Higgins') to make it smoothly apply to higher HD enemies?

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    1. That's a hard question, and I bet there's a bunch of different interpretations around that. Given I had to code something concrete in my Arena simulator I actually spent months this year going back and forth with different iterations. Super problematic!

      What I personally have coded at the moment is: if the enemy is mostly 1 HD, then start doing sweep attacks. Every attack goes at a random opponent. If one is identified with 2+ HD, then the attack sequence just stops.

      A different interpretation would be to require that the high-level types on each side must seek each other out and avoid the mooks. E.g., there's support for that in Swords & Spells.

      And there's also a cornucopia of methods for scaling it a bit more smoothly. E.g.: (a) bump up the HD limit by fighter level, (b) get attacks by ratio of level/HD, (c) distribute pool of damage across opponents, etc. There's so many iterations of that I'd be uncomfortable picking one and putting it in my house rules (no consensus).

      But: I've never heard of sweeping on top of regular attacks, my understanding is it's a binary mode selector of "fighting normals" or not.

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    2. Yeah I think my druthers is either:

      You can't do it if there is a greater than 1 HD in melee with you. (sort of incentivizes calling out bigger foes without specifically dictating character actions)

      or

      You can do it with mixed and 1HD+ targets are just skipped/ignored. (which basically would give the big guys a free attack while you take care of the mooks?)

      I would probably go with which ever ends up being easier to remember, adjudicate at the table?

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    3. Very interesting, thank you! I'm considering random targeting in melee for my next campaign to add chaos and prevent 3e/4e style focus attacks on enemy leaders (which requires elites and solos which all but requires inflated hit points).

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    4. I basically agree with Baquies above that I've be likely to fall into some habit at the table that's convenient. I'm kind of torn about whether PCs should be required to carve through the mooks before getting to the boss or not (certainly helpful to Wizards with guards).

      While the random-attack assignment is specified in the 1E DMG, and it was the easiest thing to put in my simulator code, I'll confess that I never saw anyone run that way until a video of Jim Ward running Greyhawk on YouTube. Link

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  10. Combined with random targeting in melee, one could allow a fighter to attack [level]HD. If the roll indicates you attack the ogre first, no more goblins (unless you are level 5+).

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  11. In order to smooth the discontinuity, I'd be tempted to let fighters use their sweep attack on targets with N>1 HD, but make it use up N of their attacks. For example, if you had 6 attacks, you could sweep through three 2 HD targets, or two 3 HD targets.

    To avoid abuse, I'd say if you choose to sweep, then you need at least as many attacks left as the HD of the next target. For example, with 6 attacks, the 5 HD monster takes 5 of them, and with 1 attack remaining you could hit a 1 HD enemy but not a 2 HD enemy.

    The player wouldn't need to know the targets' HD, the GM could just say "your sweep manages to get through the first 3, before it stops".

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