I must create a system, or be enslaved by another man's. I will not reason and compare: my business is to create.

- William Blake

Tuesday, September 19, 2023

Critical hit checklist

Continued from here.

As you can see, I'm a bit obsessed with critical hits.

What if, instead of a random table, we had a checklist of circumstances to modify your damage on a critical hit?

Add that to a small formula, some randomness, and, again, we can have an incredibly detailed system without wasting time or brainpower.

What's best, we can get the "critical hits" we see in the Conan stories or the death of Smaug.

Remember, this is the occasional slow motion close up you see in movie battles. This is NOT something you check often!

This system assumes ascending AC.

It takes place when you roll a natural 20.

First, deal maximum damage to you foe. 

If your foe is still alive, go to phase A. 

If your foe is dead but you have another foe within reach, go to phase B.

Otherwise, maximum damage is all you get.

Phase A (brutal hit)

A) Roll 1d10, and add it to your original roll.
B) Subtract your foe's AAC.
C) Add your Speed Factor.

If the result is less than 20, go to phase B. Otherwise:

20+: max damage x2.
30+: max damage x3.
40+: max damage x4.
Optional: natural 10 on the d10: roll again with a +10 bonus "ad infinitum".

[Optional] If your foe is STILL alive, the DM can decide, on a scale of 1-10, how adequate your weapon is to kill your foe with one blow, give the opponent's armor, size and composition, and add it to the table above.

This is very subjective, of course.

E.g.: a dagger is a terrible weapon against a skeleton, someone wearing armor, or a giant enemy (maybe 1 or 2), but deadly against unarmored opponents (9 or 10) while a two-handed mace is good against all kinds of armor (maybe 7 regardless of armor). A warpick is made specifically to defeat armor - so maybe give it a 10 against chain or plate, but only 6 against unarmored foes, and even less against big soft enemies such as a gelatinous cube.

Phase B (quick hit)

Roll a d10 (or use your roll from phase A if you've been there) and compared it to your SF.

If your roll is equal or greater than your SF, you can attack the same foe or another foe within reach. 


Some examples 

A) Abelard rolls a natural 20 while fighting an ogre (19 HP, AC 14). His attack bonus is +3.

His sword normally deals a maximum of 9 damage (1d8+1), not enough to kill the ogre.

In phase A, he roll 1d10 and gets a 6, resulting in:

A) 23+6 = 29
B) 29-14 [AC] = 15
C) 15+5 [SF] = 20

This means double damage - 18 points - still not enough!

The DM could assign a 1-10 rating to his weapon, but in this only a 10 would make a difference and the DM decides his sword is not quite perfect to kill an ogre with one blow (maybe a two-handed sword would).

Still, in phase B, he gets another shot at the ogre due to his sword's speed factor.

B) Boris, the thief backstabs another ogre with a dagger!

His attack bonus is +2, but he gets +4 and double damage for the sneak attack (2d4, a maximum of 8).

In phase A, he rolls a 4, getting:

A) 26+4 = 30
B) 30-14 [AC] = 16
C) 16+2 [SF] = 18

Oh no! "Only" maximum damage.

But the GM decides that the dagger is ideal for backstabbing, even though far from ideal to kill an ogre with a single hit! Still, a rating of 2 is enough to double damage to 16, which almost does it.

And since the dagger is a very fast weapon, he still gets another attack in phase B!

C) Carolus the Cleric is fighting a knight in plate armor (AC 17, 13 HP) and rolls a natural 20.

His attack bonus is only +2 and he rolls a 3.

The total in phase A is 22+2-17+7 = 14.

Only maximum damage. 

Fortunately, the mace is a great weapon against plate, so the DM adds 7 to the result - double damage!

Unfortunately, the one-handed mace deals only 6 maximum damage, so the total of 12 is not enough to kill the knight.

And since the mace's SF is 7, Carolus does not get an extra attack.

Still - the knight has 1 HP. 

Will he run, or try his luck with his 1d8 sword against Carolus' chain armor?

D) Can we kill Smaug with that? Let's say, AC 20, 45 HP.

Not easy.

Assuming a level 10 warrior (+7 to hit).

Consider the magic arrow plus exceptional strength (and any archery specializations etc.) to give the archer a +6 bonus to attack and damage (maximum damage 12). 

Still not enough.

Unless the dragon has a soft spot with lower AC [12?]... and you're using the PERFECT arrow, made to kill this specific dragon (+10).

Now we'd have 20+7+6+10-12=31, plus 1d10.

The chances of quadruple damage is about 20%. 

But the chances of getting a nat 10 in the first place is only 5%...

So, about 1% chance.

Eh, not bad.

What about the NPCs?

Same deal.

But if you want to simplify things, just max damage and an extra attack is good and balanced enough.


As you can see, all crits are devastating or nearly so - especially if your armor isn't great.

And the optional 1-10 bonus requires some adjudicating.

This is probably too much for B/X, unless you want a really gritty game. 

You could reduce the numbers to your liking - for example, ignoring the optional bonus to make things simpler, or reduce the range to -5/+5 (defaulting to 0).

Come to think of it, ignoring it might be better. The SF is enough to make up for it, barring specific circumstances.

Anyway, in Dark Fantasy Basic, PCs are a bit tougher than average (ogres too - I use 4d10+1 HD for them, so about 23HP) and my campaign is around level 5 now.

Guess I'll give it a try!


  1. Just remember what ol' Gary said. If you can crit the monsters, the monsters can crit you!

    1. Yes! I think giving extra attacks to monsters is not a bad idea; weak monsters will not usually be a menace, and strong ones are usually outnumbered.

      Maximum damage, OTOH, is fair game, since it is already a possibility with every attack.

  2. I like the idea, but I think that you're right that the full version is too busy for B/X. Maybe removing the optional bonus and the d10 roll would help: you'd want to change the scale to something like 10+ for x2, 15+ for x3, etc.

    Is there already a term for the difference between the final result of your attack roll and the target's AAC? There should be, because it's a really useful number for adjudicating something like extra damage. Maybe "hit margin" or "success margin"?

    Another option: take out any doubling or tripling, and make the extra damage from a crit = max damage + SF + hit margin. The extra damage would be entirely due to how well you hit and how heavy/slow your weapon is.

    And you could do additional extra damage on crits by taking an extra action/round to aim (e.g. for that important shot at Smaug) or to wind up for a big swing (like a haymaker). Maybe modify that aim/wind-up bonus by your level: +1 or +2 aim/wind-up damage per level? That level-10 warrior attacking Smaug could get an extra +10 or +20 damage on a crit by waiting for the perfect shot. (That looks like a lot, but he still has to roll that nat 20 to get it.)

    1. I really like these ideas, as I'd prefer the system to be as simple as possible.

      "Max damage + SF + hit margin" is very good and straightforward.

      OOH, it allows Conan to kill an unarmored aristocrat with a punch.

      OTOH, it lessens the differences between weapons (especially magical ones such as a +3 sword), and, as you noticed, requires additional rules to kill Smaug.

      Aiming is definitely a good idea too!

      TBH, it is hard to make a system that is BOTH detailed and simple. But I keep trying! ;)

  3. I just use exploding dice for damage. 20 is no longer significant, simply rolling maximum damage is a crit, keep rolling and adding until you stop rolling max on the die. Really easy, and gives that nice you never can tell, you might be able to down Smaug effect. Also nice is that a priori it only increases the expected damage by around 1 (depending on die size) and it preserves the order of the dice (d4 is still worse than d6, even though it's chance to crit is slightly higher)

    1. I like the simplicity of this rule and the fact that it is only 1 point more damage on average. OTOH natural 20s are cool too.

    2. You could keep nat 20 as automatic hit regardless of AC (depending on whether that's even a consideration in your system). I do kind of like that it eliminates the slight oddity that with a 20-is-crit then with very high AC *if* it's a hit it's likely a crit.

    3. Nat 20 as automatic hit is not a consideration in 99% of the battles, I think. In B/X you hit plate+shield on a 17+ by level one.

      Maybe nat 20 as automatic maximum damage, thus allowing you an immediate re-roll, would be a good idea.

      Simple, keeps the possibility of infinite damage, but doesn't affect average damage by much.