## d20 Fast Mob Attack Rules

A horde of kobolds hurl spears at a ranger. Masses of brainwashed soldiers open fire on your friendly neighborhood superhero.

Rolling for mobs of weak attackers can eat up game time. It’s doubly bad since a weak attacker probably has a low chance to harm the target, so you are making lots of rolls for a low probability event.

These rules speed up the process. They work best when the attackers have the same stats (or can be considered to have the same stats to speed things up) and when attack and defense bonuses for both sides are basically the same from round to round. If those numbers shift, you have to recalculate.

1) Determine the DC for a single attacker to hit the target.

2) Subtract the DC from 21. This is how many different rolls on a d20 will hit.

3) Divide 20 by the result. This is how many attacks have to be made each round to hit once on average. We’ll call the number of attackers it takes to meet this number a “gang.”

*Example:* Rumples the Ranger has AC 18, and the pirates have +1 to hit, so the DC to hit is 17. 21 minus 17 is 4, so 4/20 rolls on a d20 will hit (17-18-19-20). 20 divided by 4 is 5, so if there were five pirates they would hit about once per round, missing the other four times. Versus Rumples every five pirates = one pirate gang.

Now that you know how many attackers are needed to score a hit on average, just divide the attackers into gangs and that’s how many hits they get each round. If five pirates are needed to score an average of one hit per round and twelve pirates are attacking, just round down and call it two hits per round (12/5 = 2.4). Now you just need to roll damage.

It may seem a little mathy at first, but if you take a few seconds and do this calc at the start of the fight the following rounds of combat will go much more quickly. Different targets (aka PCs) will have different numbers so calculate for each one. As opponents are killed all you have to determine is how many gangs can be made from the ones that remain.

### Adding Randomness

If you miss the randomness of rolling for attacks you can use a single roll to simulate randomness for all the attacks. After all, dice are fun.

Roll a single d20 for each target being attacked regardless of how many gangs are attacking.

*roll hits*

1-5 no hits

6-15 normal hits

16-20 2x hits

*Example:* Versus Rumples five pirates makes a gang. Twelve pirates are attacking, so that’s 2.4 gangs, which we’ll round down and call two gangs. Round 1 we roll a single attack and get a six (normal hits) so Rumples takes two hits. After rolling damage Rumples is doing fine, so Round 2 we roll another attack and get a 17 (2x hits) so he takes four hits. Things are starting to look bad for Rumples.

If you like more extreme results and think 20’s and 1’s should be special, use this result table instead:

*roll hits*

1 no hits, attackers are disorganized and automatically miss next round

2-5 no hits

6-15 normal hits

16-19 2x hits

20 4x hits

Statistics note: The more dice you roll, the more the results become average. We’re only rolling one die, which may seem to create extreme results but the distribution of the results has already been spread to mimic the results if you rolled a bunch of attacks separately.

### Fractions

If you want to simplify your calculations you can drop or round off fractions. Fractions are most important in cases where the number of hits is low. If the attackers can get 1.5 hits per round, the .5 is critical. If the attackers can get 3.5 hits per round, the .5 is less important.

If the number of hits is less than 1 the attackers will normally not hit every round. You can do a rough calc and average the hits across rounds (.5 will hit every other round).

Another option is to roll for the fraction each round as a separate check. Just take the decimal and see if you roll that or less on a d10 each round (or a d20, counting 11-20 as 1-10). If you do, it’s another hit. You can roll both the d10 and the d20 for the main attack check at the same time.

Now go swarm those players with hordes of cannibals!

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Nathaniel Eliotsays:I’ve run some numbers for a similar system with a slightly different dynamic, which keeps the percentages very roughly balanced versus standard combat:

The base gang size is just 4. This makes things numbers simple, and is a realistic number of same-size opponents to face in a mob combat situation. Two checks are required for a character surrounded by opponents on all sides, three or more for larger gangs of different sized creatures.

Subtract the attackers bonuses from defender’s AC; this is the attackers to-hit target, so if it’s over 20 they won’t hit except on a critical. Roll a d20+10 (or tak0e a 10 for a total of 20), add +2 apiece for a fifth or sixth mob member (or -2 for only three), and subtract the to-hit target. the attackers score one hit for each full multiple of five remaining. Crits occur normally, but their threat range is doubled (on both ends, so 2 or less is a crit fail). You can also total these together, for a surrounded target (2d20+20 – 2x target), or larger mobs of smaller creatures (e.g. – humans vs. a mammoth).

Attackers are four foot-soldiers, +2 to their attack from flanking, defender is a mage with some protection and Dex, AC 15: the target is 13. Taking a ten results in a seven, or one attack hitting. A 13 or above would result in two hits, and an 18 in 3 hits, while an 8 or less would be a complete miss.

A squad of eight soldiers surrounding the same mage would have a range (on 2d20) of anywhere from two crit failures to four hits (taking 10s) to six hits (36 or more).

Attackers are eleven foot-soldiers, +2 from flanking, defender is a giant in magic armor, 22 AC: target is 20. Taking a ten results no hits (20-20 + 20-20 + 20-20 = 0); roll 3d20, with results from three crit failures to five hits (58 or more).

Adamsays:#Bob the builder

What? The point of a game is to have fun, not roll dice. If the dice become detrimental to the fun it’s very good idea to replace them with something.

This system, particularily the addition of the roll modifiers is brilliant. It would probably go a step further and include that .5 no matter what, tabulating an extra hit for every odd round or otherwise, but it’s an excellent mechanic idea nonetheless. Thanks

Bob the buildersays:you, could do this…. or you fucks could stop being lazy and just roll the damn dice!!!! thats what is is ment to do, if you dont like it stop playing :0

Grafsays:Great idea.

Scholzsays:Tried to make a Trackback link to Malaanica… this doesn’t seem to offer that option. Where would I give you the link?

http://malaanica.blogspot.com/2006/02/gang-damage.html

Scholzsays:This is one side of the equation.

Can we speed up the other side of the equation (ranger versus the horde?). One method is using something like the minion rules (take 10 on attacks vs minions, fail all saves) and those look fine. What about damage?