Advanced Mob Rules | New Rules and Mechanics for Fifth Edition

Mobs are fun. After all, every player with a high-level character imagines what it’d be like to run through a mob of a bunch of CR 1/8 weenies.

Logistically, though, it’s a pain, especially for the GM. For example, if you wanted to challenge a group of four 10th-level adventurers with kobolds (CR 1/8), you would have to toss 48 kobolds at them just for it to be a “Medium” level challenge. I promise you, there’s no DM on earth that wants to run that combat.

Now, the DMG gives some rules for running mobs, mostly in the amount of damage that they do. And that’s helpful. But it still doesn’t address the insane number of hit points a mob’s going to have, the fact that the characters can only attack so many at once, and other complicated issues that will bog down playtime considerably. A Medium-level encounter that’s destined to only hand out 300 XP per character at level 10 just isn’t worth the trouble.

What follows is my solution for this conundrum: advanced mob rules.

Treating Mobs like Complex Traps

The best way to deal with mobs is to treat them like a terrain hazard or a complex trap. XGtE has some great rules for complex traps. After all, when dealing with mobs, that’s exactly what you’re fighting: a complex trap. Therefore, all you really need to do is to tie the elements of the complex trap to a mob of monsters, and presto: it’s an easy-to-run encounter.

Let me break it down for you.

Initiative. The mob has its own turn in initiative order. Fast mobs (those with high Dexterity or alertness traits) attack on initiative count 20, whereas slow mobs attack on initiative count 10 (creatures such as zombies or oozes). Very fast mobs attack on initiative count 20 and 10 (creatures with extremely high Dexterity, legendary creatures, etc.)

Active Elements. Active elements likely include attack methods for the mob itself which it deals during its initiative.

Dynamic Elements. Like traps, a dynamic element is a threat that arises or evolves as the trap functions. Usually, these dynamic elements take effect at the end of each of the mob’s turns or in response to the characters’ actions.

Constant Elements. A mob poses threats even when it’s not taking its turn. The constant elements explain how these parts of the mob function. For example, when a mob surrounds a group, it’s likely that moving through the mob becomes difficult, creating difficult terrain or relying on Athletics or Acrobatics checks to move through them. It can also include extra attacks by the mob.

Countermeasures. Finally, the countermeasures for a mob usually involves attacking it but may include other means of destroying it (such as scaring off the mob, etc.)

Additional Items. Mobs of monsters are living things. As such, they have abilities, saving throws, and skills. In addition to the aforementioned elements, I’ve included a few features from monster stat blocks as well.

Running a Mob

A mob functions in play much like a legendary monster. When it begins its attack, the mob’s active elements act according to its initiative. On each of its initiative counts, after all creatures with the same initiative count have acted, the mob’s features activate. Apply the effects detailed in the mob’s description.

After resolving the effects of the mob’s active elements, check its dynamic elements to see if anything changes about the mob. Many mobs have effects that vary during an encounter. The creatures may work themselves into a frenzy, dealing more damage as it remains active, or call upon additional creatures to join the group.

The mob’s constant elements allow it to have effects when it isn’t the mob’s turn. At the end of each creature’s turn or when a creature takes an action or moves, look at the mob’s constant elements to see if any of their effects are triggered.

Mob Size and Space

Since mobs represent large groups of creatures, the typical creature size and space rules don’t apply to them. For example, fifty kobolds are going to fill way more space than that of a gargantuan creature (which would normally only fill 16 squares). The Mob Size and Space table below demonstrates how much space mobs fill.

To make things easier, for rooms that fit roughly the square or hex count listed on the Mob Size and Space table below, assume that the mob fills the entire room. For larger rooms or outside areas, you can use a single large miniature to represent the entire mob.

Mob Size and Space (Medium or Small Creatures)

Mob Size Creatures Space: Squares Space: Hexes
Standard 16-25 16 squares (4 by 4) 12 hexes
Massive 26-50 25 squares (5 by 5) 19 hexes
Gigantic 51-75 36 squares (6 by 6) 27 hexes
Enormous 76-100 49 squares (7 by 7) 37 hexes or more

Example Mob

The following mob can be used to challenge characters.

Kobold Mob

When pressed, kobolds team up in massive hordes, using their overwhelming numbers to take down even the most dangerous foes. These mobs can contain as few as 16 kobolds or as many as 100. The following description details a massive mob of 50 kobolds.

Kobold Mob

Massive mob of Small humanoids (kobold), lawful evil


Armor Class 12

Hit Points 250

Speed 30 ft.


Abilities. Str 7 (-2), Dex 15 (+2), Con 9 (-1), Int 8 (-1), Wis 7 (-2), Cha 8 (-1)


Condition Immunities charmed, frightened, grappled, paralyzed, petrified, prone, restrained, stunned

Senses darkvision 60 ft., passive Perception 8

Languages Common, Draconic

Challenge 10 (5,900 XP)


Trigger. When the characters enter the room where the mob is hiding, the mob attacks.

Initiative. The mob acts on initiative count 20.

Active Elements. On its turn, the kobolds attack each hostile creature within 30 feet of them using their slings and daggers.

  • Attack (Initiative 20). The mob attacks each creature that it can see within 30 feet of its location. The mob’s attack bonus equals +4 plus +1 for every 25 hit points the mob has. On a hit, the mob deals 1d4 bludgeoning damage or piercing damage (GM’s discretion) plus an additional 1d4 bludgeoning or piercing damage for every 25 hit points the mob has.

Dynamic Elements. The mob becomes more dangerous the longer it remains active.

  • Reinforcements. The mob calls in additional assistance. At the end of the mob’s turn, it gains 25 temporary hit points. After the mob uses this dynamic element 5 times, the element ceases to function.

Constant Elements. The mob poses not only poses a threat to the characters’ health but also acts as difficult terrain.

  • Mob. The mob can occupy another creature’s space and vice versa, and the mob can move through any opening large enough for a Small kobold. The mob has advantage on Strength and Dexterity ability checks and saving throws. Effects that use an area of effect deal double damage to the mob as long as the mob has half of its hit points or more.
  • Difficult Terrain. To move through the mob, a character can attempt to overrun the mob or tumble through it. To overrun, a character must use its action or bonus action to make a DC 13 Strength (Athletics) check. On a success, the character can move through the mob as if it were difficult terrain until the end of its current turn. Similarly, to tumble, a character must use its action or bonus action to make a DC 17 Dexterity (Acrobatics) check.  On a success, the character can move through the mob as if it were difficult terrain until the end of its current turn.
  • Attacks. Any creature that ends its turn in the mob’s area or within 30 feet of the mob and the mob can see it, is targeted by an attack: the mob’s attack bonus equals +4 plus +1 for every 25 hit points the mob has. On a hit, the mob deals 1d4 bludgeoning damage or piercing damage (GM’s discretion) plus an additional 1d4 bludgeoning or piercing damage for every 25 hit points the mob has.
  • Pack Tactics. As long as the mob has 25 hit points or more, it has advantage on its attack rolls against creatures that share the same space as the mob or are within 5 feet of the mob.
  • Cowardly. If the mob starts its turn with 125 hit points or less, roll a d20. On a result of 12 or higher, the mob disperses, fleeing in multiple directions at once. At the GM’s discretion, 2d8 kobolds may remain in the area. These remaining kobolds will likely grovel and beg for their lives.

Countermeasures. As the mob loses hit points, it loses its ability to harm its targets.

  • Attack. A creature sharing the same space as the mob or within reach or range of the mob can attack the mob. Reducing the mob’s hit points reduces its attack bonus and damage (see the mob’s attacks, above).
  • Exposure to Sunlight. If the mob is exposed to sunlight, the mob has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

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