Handling Multiple NPCs' Actions with a Single Die Roll
[in D&D 3rd ed.]
by Joel Hahn
The following is intended to be compatible with D&D, but can be used,
usually with no or little modification, with just about any RPG.
Have you ever tried to DM a party caught in an ambush of 50 archers but
couldn't figure an quick, easy way to resolve the NPC's turns in under two
hours each, but also don't want to crack open the Battlesystem rules? Or
had 10 Imperial Guards try to climb a rock face after our heroes but didn't
want to roll skill checks for each and every one?
Here are two solutions for using one die roll to determine multiple actions
of NPCs:
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Method 1) Use Torg's "Many on One" table, modified slightly
#Char Bonus | Result #Succ
----- ------ | ------ -----
1 +0 | DN 1
2 +2 | DN+2 2
3-4 +3 | DN+4 3-4
5-6 +4 | DN+6 5-6
7-10 +5 | DN+8 7-10
11-15 +6 | DN+10 11-15
#Char = number of characters with equal modifers whose actions will
be resolved with this roll
Bonus = a bonus applied to the roll
Result = How much the die roll beats the Difficulty Number (DN) by
#Succ = number of characters that succeed at the action
To use this table, first group the NPCs into groups with equal attack bonuses
and/or other modifiers (e.g. fighting on higher ground), and then split those
groups, if necessary, into groups of 15 or smaller.
Check the left side of the table to see what additional modifier will be
applied to the die roll due to number of characters attempting the action.
Roll one d20, applying the modifier from the "Bonus to Hit" column, as well
as any situational modifiers which all of the NPCs will have.
Compare the resulting total to the third column. The DN is the number
needed for a single person in the same situation to succeed. For attacks,
the Difficulty Number is the opponent's AC. The number in the same row
under #Succ is the number of NPCs that succeed. When that number is a
range, the DM either chooses an number appropriate for the given situation,
or flips a coin or rolls a d4 or d5 to determine exactly how many NPC's
succeed.
Example #1: Ten 1st-level archers are firing on Rast, a fighter in chainmail
with an AC of 15. The bonus for 10 NPCs is +5. The roll comes up 9.
9+5 = 14, but the archers needed a total of 15 for any of them to hit, thus
they all miss. However, on the second turn, the die comes up 15; 15+5 = 20,
which beats the number needed to hit Rast by 5. The DN+5 line under #Succ
is 3-4, so 3-4 of the ten archers succeed. The DM decides that 4 archers
actually succeed and rolls damage accordingly.
Example #2: Five guards attempt to pursue our heroes over a thin foot-bridge
across a chasm in the heart of an underground complex. The DM determines
that successfully crossing to the other side has a DN of 14. The bonus for 5
NPCs is +4. The DM gives the guards a bonus of +1 because of their familiarity
with the bridge. The roll comes up 6. 6+4+1 = 11, which is not enough for any
to succeed, so they all slip and fall screaming into the bottomless chasm. If
the roll had been a 19, 19+4+1 = 24; the roll would have beaten the difficulty
of 14 by 10, so all five would have succeeded.
Since this system does not take automatic success on a natural 20 into account,
this system works best if you use a house rule that die results of 20 are
rerolled and the result is added, instead. It still works under the standard
system, but doesn't allow for automatic success against impossible odds.
This system can also be used to determine the outcome of PC actions, though
I do not recommend it for such, as players usually like to determine success
& failure for themselves. If you are running a campaign where the DM is the
only one rolling dice, then this may be something to look into, especially
in situations such as scaling a rock face or simple combats involving
equal-ability party members and a single opponent.
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Method 2) Multiple NPCs Success Table
For those people who really like tables (and a little bit of easy
calculation), here's another solution, based on probability theory, to the
problem of resolving many NPC's actions, especially attacks.
<-10 -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0
0 1-99 1-97 1-77 1-59 1-44 1-33 1-24 1-17 1-12 1-8 1-5 1-3
1 100 98-99 78-98 60-92 45-83 34-74 25-63 18-53 13-43 9-34 6-26 4-18
2 * 100 99 93-98 84-98 75-94 64-90 54-84 44-76 35-68 27-59 19-50
3 * * 100 99 99 95-98 91-98 85-97 77-94 69-91 60-87 51-82
4 * * * 100 100 99 99 98-99 95-99 92-98 88-98 83-97
5 * * * * * 100 100 100 100 99-100 99-100 98-100
1 2 3 4 5 6 7 8 9 10 >10
0 1-2 1-2 1 1 1 1 * * * * *
1 3-13 3-9 2-6 2-3 2 2 1 1 * * *
2 14-41 10-32 7-24 4-16 3-10 3-6 2 2 1 1 *
3 42-74 33-66 25-57 17-47 11-37 7-26 3-17 3-8 2 2 *
4 75-95 67-92 58-88 48-83 38-76 27-67 18-56 9-41 3-23 3 1
5 96-100 93-100 89-100 84-100 77-100 68-100 57-100 42-100 24-100 4-100 2-100
Start with 0. Subtract any penalties and add any bonuses to the success
roll[1]. Find the column marked by the result. Divide the NPCs into groups
of 5 (or multiples of 5)[2] so that all of the characters in a group will
use the same column[3]. Roll d100 for each group and find which row the
result is in. That is the number of characters who succeed.
[1] Use -(DN-10) as a penalty; for combat, this is the target's AC.
[2] If using multiples of 5, be sure to multiply the row headers by the same
amount.
[3] If a group has less than 5 NPCs in it, you can either roll separate
checks for each as per the standard rules, or scale the total in that group to
the table:
If there are 2, treat results of 1-3 as 1, and 4-5 as 2
If there are 3, treat results of 1-2 as 1, 3-4 as 2, and 5 as 3
If there are 4, treat results normally, except for 5, which is treated as
a result of 4.
Example #1: 5 tenth-level archers are attempting to fire at Rast, a fighter
who has an AC of 21 due to his enchanted full plate armor. The archers'
total attack bonus is +9. 21-10 = 11; 0 -11 +9 = -2. The DM rolls d100;
the result is 37. A 37 in the -2 column shows that 2 of the 5 succeed, and
the DM rolls damage accordingly.
Example #2: 14 tenth-level archers are attempting to fire at Rast, a fighter
who has an AC of -1 due to his enchanted full plate armor. The archers have
a total attack bonus of +9. The DM splits the archers into a group of ten
and a group of four. As above, the -2 column is used to determine the
result. The DM rolls 2d100, one for each group. The first roll is 72, the
second is 20. Therefore, five or six archers (3 is treated as 5-6 for the
purposes of a group of ten NPCs) from the first group and one from the second
group succeed, The DM decides that five from the first group actually succeed,
making a total of six successful attacks. The DM rolls damage accordingly.
Example #3: Five guards attempt to pursue our heroes over a thin foot-bridge
across a raging river in the heart of an underground complex. The bridge is
slippery from the spray from the river, so the DM assigns a balance check DN
of 17. The guards all have DEX scores between 10-11, so there are no positive
modifiers for their balance check in this case. -(17-10)=7 means the -7
column is used. As you can see from the table, the difficulty is so great that
it is impossible for all five guards to succeed. The DM rolls a d100 and gets
a 53, which means that only 1 of the guards succeeds; the other four fall into
the swift current and are swiftly carried away to parts unknown.
Like the first method, this system does not take into account the possibility
of an automatic success, even for otherwise impossible to reach DNs, based on
the die result.
This method, like the first, can also be used in some circumstances to
determine the outcome of PC actions.
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If you have any feedback, especially if it regards Method #2, please either
mail it to Aardy, or post it to rec.games.frp.dnd
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