D&D 5E How to handle massive oncoming swarms

[MNblockhead]

I'm running an adventure in which there are a number of places where you can run into just huge numbers of monsters that will continue to stream.

For example, there is a subterranean river where these evil Tsathoggua frog-men abominations will keep coming at 2d6 per round up to 500 of them.

In this case you have to keep fighting them off until you get the McGuffin and then get out. They won't chase you out of the area. I suppost the writers gave a figure as some players may want to cleanse the area of the evil.

In another situation, there was a cursed crypt where a Tsathoggua priest gave his life by imbibing an elixer of all-seeing doom and he was buries and a hermetically sealed vault. If the players break into it, this bubbly mass of liquid flesh with eyes bubbling out of it which hatch into killer frogs is seen. The killer frogs keep coming and unless you find a way to stop them, they will overrun the country side. There are 666 of them. In this case the players used a mixture of a cube of force to block the entrance and protect themselves, fireballs, and spirit guardians to destroy all the frog. In this situation, I went with average damage and did some simple on the fly math to determine how many rounds and spell slots were needed.

I know that this is a what swarm stat blocks are for, but swarms don't capture the continual streaming of monsters.

I'd be interested in ideas on less grindy, more fun ways of handling these situations. The basic requirements for a mechanic for this would be that it would have to resolve over-all length of time, how much of a parties resources are used, give players agency in determining how they will handle the situation, and handle damage output to characters who don't have anything protecting them from attacks (e.g. using something like mob rules).

My thought is to use something like 4e skill challenges. First, determine the worst case scenario, second the best case scenario, and third the overall challenge. Let each player describe how they are contributing. Each makes a roll and determine the outcome based on the rolls. I worry that if loss of HP or even death is possible, that players would not be satisfied with that being handled by one or a couple skill checks. At the same time, spending half an hour or more grinding through a stream of monsters is boring.

 

[aco175]

I'm not sure if minions like 4e would make it less a grind. You could have waves every other round or every 3 rounds. If the PCs kill the first batch in a round or two, they have a 3rd to act that is not tied to combat. You could also introduce a skill check to drop a boulder over the entrance or other blocking terrain. I'm not sure that D&D does waves of monsters right.

 

[MNblockhead]

I'm not sure that D&D does waves of monsters right.

Do you know of any systems that you think do handle it right? If so, how do they handle it?

 

[Lanefan]

I'm not sure if minions like 4e would make it less a grind. You could have waves every other round or every 3 rounds. If the PCs kill the first batch in a round or two, they have a 3rd to act that is not tied to combat. You could also introduce a skill check to drop a boulder over the entrance or other blocking terrain. I'm not sure that D&D does waves of monsters right.

I think D&D does waves of monsters just fine, provided both the DM and the players are patient enough to grind it all out.

What D&D doesn't do well are shortcuts around the grind.

 

[cbwjm]

You could limit the maximum number available to attack the PCs at one so that at most 12 fishmen are actively attacking the PCs. If they kill 3 then 3 more pop up to take their place. I'd have them always come from same spot in the area so that it might take a round for the enemy to reach the PCs. You could also have no more than a certain amount be able to spawn at once so a maximum of 12 with additional units coming in at 2/round. If the PCs kill 3 or more then they'll start to slowly stem the tide of incoming monsters.

 

[Lanefan]

You could limit the maximum number available to attack the PCs at one so that at most 12 fishmen are actively attacking the PCs. If they kill 3 then 3 more pop up to take their place. I'd have them always come from same spot in the area so that it might take a round for the enemy to reach the PCs. You could also have no more than a certain amount be able to spawn at once so a maximum of 12 with additional units coming in at 2/round. If the PCs kill 3 or more then they'll start to slowly stem the tide of incoming monsters.

The PCs could achieve something similar if they're able to establish and hold a choke-point e.g. a doorway or narrow passage. This might not stem the tide but it'll at least slow it to a more manageable rate.

 

[MNblockhead]

Thanks for your comments. I guess I'm looking for fun and fair ways to avoid having to resolve hundreds of enemies in a trickle.

If I have, say 100 enemies. Well that's not that hard using swarm stats, DMG optional mob rules, and VTT automations for area of effect spells.

But if I have 500 or more monsters coming in at a trickle (e.g. 2d6 per round), I find that unsatisfying. ESPECIALLY when players are smart and set up choke holds and spirit guardian blenders, etc.

I'm trying to come up with some heuristics for these scenarios. E.g.,

If there is little to no chance of the party taking damage (e.g. they've set things up very intelligently with terrain advantages, walls of force, and/or areas of effect that are going to kill everything coming their way with them picking off the stragglers easily) then I'll just handwave it and simply make a rough calculation on how long it will take.

If the mobs are powerful enough to hurt the party in mass but the trickle is so small that the party is picking everyone off before they can really pose a threat, I will say that even dumb animals may pool together until their are enough of them to make a swarm and attack. That way there are are a smaller number of combatants (swarms) that the party can fight. Much more interesting and easier to manage. Instead of 2d6 giant rats or killer frogs every round, say that everyone 1d6 rounds a new swarm appears. Divide the total number of baddies in the pools into a number of swarms that seems right for their size and type. I'd use story math more than trying to be exact.

For more powerful enemies where swarms would make them less dangerous, I would instead say that they hold back until they have sufficient numbers to do at least a bit of damage each round to the character with the highest A/C in the party based on the DMG mob rules. So if it takes at least a 10-unit mob to make one auto hit on an A/C 22 character, I would have them at least pool numbers until that number. Even better pool the mob until there are enough to auto-hit almost every character. I might also use the 4e style mob rule where if you hit one, it dies, rather than tracking hit points. This really only works where there is sufficient space for it. And my players are smart enough to not expose themselves to getting mobbed like this. I actually find it rare these days where I can apply the option DMG mob rules because my players have learned to avoid putting themselves into positions where they can get mobbed.

 

[Quickleaf]

Years ago I tackled this question for a 4th edition party running through Dragon Mountain which featured lots of kobolds. Like you, I was looking to allow for some familiar strategies of fighting a monster to feel relevant while also offering more opportunities for interesting challenges & creative lateral thinking. Besides minion rules and a bunch of other devices, I created a Kobold Horde stat block which emphasized unusual ways of interacting.

It had the following traits (translating for 5e parlance):

• From All Sides: The kobold horde occupies an enormous undefined area, and it can move into and through enemies' spaces and does not provoke opportunity attacks. It is considered adjacent to all enemies in the encounter at all times, and has advantage on melee attacks thanks to Pack Tactics.
• Swarm Attack: At the start of each of the kobold horde's turns, all hostile creatures in the area are grappled (escape DC #). A creature starting its turn grappled by the horde takes 5 bludgeoning damage.
• Horde Immunities: The kobold horde is immune to all conditions that don't originate from area effects. If it would be incapacitated, the swarm instead lets go of the nearest grappled creature.

It also had the following actions/bonus actions/legendary actions:

• Overwhelming Surge: The kobold horde makes an attack against each creature in the area. If a creature has been disarmed of a magic weapon, then one of these attacks is made with that weapon.
• Swarm the Fallen: The kobold horde targets each prone creature in the area with a special attack that disarms the creature of a held item.
• The Horde Presses Down: Each creature in the area must choose once check to make (DC X) to resist the horde: Athletics, Perception, Stealth, or Survival. A failed check indicates that creature has been separated from the rest of its party, in addition to the following:
  • If the creature fails Athletics, it is restrained until the end of its next turn and the kobold horde gets a free attack against it.
  • If the creature fails Perception, it is forced into a trapped passage (roll on Random Trap Table) until the end of its next turn.
  • If the creature fails Stealth, any light source it has is lost and it is forced into a dark passage until the end of its next turn.
  • If the creature fails Survival, it is forced into a tight passage until the end of its next turn – its speed is halved and attacks against it have advantage due to squeezing, and its attacks with non-Light weapons suffer disadvantage.

 

[NotAYakk]

Here is a sketch of simulationist mob rules:

D&D 5E - Handling mobs

I really enjoy the use of minions in 5e, but like the sane, rational person I am, I don't want to deal with each individual minions attack and damage rolls. I also don't like the exactness of the DMG's rules for handling large groups of enemies. So I've stolen some concepts from the Conan 2D20...

www.enworld.org

you work out their HP/square and have damage/AC/save DCs/etc scale with the number of attackers in a pretty simple manner.

HP damage instead kills squares of it. You don't track individual monster HP, just squares. And you round HP/square to something nice.

When someone throws a fireball that hits 20 squares of it, you roll 8d6*20 and give them a +10 (+1 per square beyond the first, capped at +10) save bonus (this represents that the ones in front give cover to the ones behind). They pass (naturally) and take 8d6*10, or 280 damage. If they have 20 HP/square, that is 14 squares dead.

Similarly, their attacks are massed; every doubling of attackers gives them an extra set of damage dice, and they get +1 to hit for every attacker beyond the first (up to +10).

So if you are surrounded by 8 of them, they get +7 to hit and deal 4[W]+stat damage on a hit.

In this model, players who want to fight it have to actually fight it, but we reduce interaction to 1 roll per interaction, instead of 1 per monster.

A fun part of this is you can simulate infinite hordes this way; like a wave of zombies. Each entrance has a number of zombie squares/round incoming (based off a choke point and how fast they move). Killing them just pushes back the wave by a certain number of squares.

 

[Shadowdweller00]

I would tend to say: Don't worry too much about specific numbers of foes. Improvise a few swarm-type stat blocks that represent different numbers of enemies. If you want it super-quick - use only one "swarm" creature and up or downgrade it based on the number of creatures that can reach the PCs at any particular time (swarm might upgrade to larger type as monsters come, or downgrade to lower if the PCs kill off or find some way to prevent enemies from reaching them easily). If you want it not-quite-so-super quick use a couple of "swarm type" monsters. Maybe give them vulnerability to AoE effects to represent the effects of having multiple component creatures. And some sort of push/grapple/trip effect to represent mass numbers.

Step 2: Consider adding an environmental effects if the creatures that can't reach the PCs have some way to attack or affect combat from a distance. For example a Dex save or take damage if they have ranged weapons/attacks. Or Str save vs push effect to represent the push of a large crowd on the PCs.