Running Horde Combat in 5e

Or how to throw 100 enemies at your players and make it fun.

Foreword: Hello! This text is an extract of the GM cheatbook I'm currently writing, I hope these rules help you create massive encounters, ones that your players will remember for years! Enjoy!

I. Damage Tracking for the Horde

• Note down the number of monsters within the horde
• Note down the hit points of one typical monster within the horde (you can round to the nearest 5 or 10 for simpler calculations.)
• Consolidate all damage received by the horde into a single hit point pool.
• When accumulated damage exceeds the hit points of one or multiple monsters, eliminate monsters from the horde and reset the damage count. Any excess damage should be carried over.

Example:

The party is engaging a horde of 20 skeletons. A skeleton has 13 hit points, but we will round it down to 10 for easier maths. There are 20 skeletons in your horde.

Your notes should look like this:

Nb: 20   HP: 10

The barbarian rushes in and lands a big critical hit for a total of 27 points of damage. With that damage, 2 skeletons go down, and damage carries over. So now your notes should look like this:

Nb: 20  18   Hp: 10  3

And you keep going until the number of skeletons drop to 0 (or the number of party members does).

II. Horde Attacks and Damage Distribution

• Assign which horde monsters attack which character. Start by looking at the situation. Does the horde have ranged attacks? Are any of the characters up front and likely to take on more than everyone else?

Our base assumption should be that the monsters attack the characters equally.

If there are fifty skeletons and five characters, ten skeletons will attack each character. If one character manages to hide from the skeletons, the skeletons divide their attacks among the rest.

If a scenario evolves and monsters can't attack, for example if there's a choke point and they don't have ranged attacks, they miss out.

Note: An isolated character that is completely surrounded can be targeted by a maximum number of 8 creatures in melee.

To save time in combat, if you are preparing to make your players take on a horde, use average damage to not spend hours rolling damage dice (see page XX),

You will be rolling a d4 for each creature attacking instead of the normal d20 to determine whether an attack hits or not. Use the following attack success rate guidelines:

• Base: 1-2: miss.  3-4: hit.
• With Advantage: Only a 1 misses.
• With Disadvantage: Only a 4 hits.
• Special Circumstances: Deduct a few successful hits.

If a creature has very high AC, or gains higher AC through casting the shield spell, something that only a 15+ on the d20 used for their normal attack roll would hit, consider making only a 4 hit.

Consider asking your players for their AC before combat so you can adjust the attack rolls accordingly.

Example:

If we take our skeletons as above, they have a +4 to hit. This means that any AC above 19 is considered very high AC for this fight, anything below is considered normal AC.

So our barbarian who charged in the fray is now surrounded by 8 skeletons. He only has 17 AC, which means we use the base rolls. We roll 8 d4s, 3 of them show a 3 or 4, so that’s 3 hits. With the average damage, it means our barbarian took 15 damage.

8 attacks and their damage wrapped up in less than a minute, very nice!

III. Handling Area of Effect (AoE) Attacks

• Determine Affected Monsters:
  • Assess the area impacted and judge the number of creatures within. Favor densely packed scenarios for dramatic effects.

• Rough estimates for creatures affected by AoE size:
  • Small AoE (e.g, flaming sphere): 4 creatures
  • Medium AoE (e.g., burning hands): 8 creatures
  • Large AoE (e.g., fireball): 16 creatures
  • Huge AoE (e.g., circle of death): 32 creatures

• Resolve Saving Throws and Damage:
  • Horde monsters are usually weaker grunts. Typically, only 1 in 4 monsters succeed on saving throws. Adjust based on context, if you throw monsters with very high DEX scores, consider making 1 in 2 succeed against DEX saves instead, etc…
  • In exceptional or heroic moments, consider having all monsters fail their saves.
  • If the AoE damage surpasses the hit points of an individual monster, remove those affected. Any residual damage after exact kills should be added to the horde's damage tally, which might result in further eliminations.

• Manage Status Effects:
  • If an AoE confers a status effect, assume 1 in 4 of the affected creatures fail and are afflicted. These creatures may be narratively described or temporarily removed from combat, avoiding meticulous tracking.

Example:

It’s now the wizard’s turn and she casts shatter. Considered a medium AoE it catches 8 creatures.

Roll for damage: 14 thunder damage.

Our horde skeletons have 10 hit points, with our rule 6 of them fail the save and 2 succeed. For 6 of them it is instant death.

So our note for the hordes would look like this:

Nb: 20   HP: 10

Nb: 20  14   Hp: 10

The remaining 2 in the AoE take 7 damage each, but we count the horde as one entity, so our notes would then look like this:

Nb: 20  14   Hp: 10  
  Damage taken: 7 + 7 = 14

Nb: 20  13   Hp: 13  6

So she killed 7 skeletons total, and damaged an 8th one.

(I’m breaking down the math to be as clear as possible, but there’s no need to do the full math on your own notes).

IV. Additional Horde Management Tips

• Narrative Focus: Emphasize the story. Instead of detailing mechanics, paint a vivid picture of hordes charging, spells detonating, and heroes standing resilient. This is an epic moment, don’t get bogged down by mechanics too much.
• Reflavoring Creatures: Use one stat block for different monsters in the horde. Describe variations in appearance or behavior without altering mechanics. You can say that the horde is composed of zombies and skeletons, but only use one of these stat blocks for your entire horde.
• Combine Horde with Single Entities: Using a horde alongside distinct creatures (e.g., a zombie horde with a werewolf who gets his own actual stat block) creates a more layered combat scenario.
  

P.S: If you use those rules in your games, leave me some feedback below, I'd love to hear your experience with them!