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New GM w / an Old Quandary: Swarms


Rules Questions


Being a novice GM, I just threw at my APL-4 party what may be the nastiest critter they have faced yet: a CR 2 swarm of rats. Now, it's not as bad as a swarm of spiders, granted. But it's nowhere near a "just to soften them up" encounter, especially since they're making Fort saves to avoid being sickened. (They did a great job on that one; the precautions they took mean that they will succeed on anything but a nat-1. Unfortunately, there have been two nat-1's in just the first round of combat!) Well, we ended for the night after the first round of combat, leaving me with a swarm of questions. {And reviewing the Rules back-history didn't help all that much, sadly.}

Let's start with the link to the Bestiary notes on the Swarm subtype; "Swarm" is near the bottom of the page.

Bestiary under Creature Types wrote:

A swarm made up of Tiny creatures takes half damage from slashing and piercing weapons. A swarm composed of Fine or Diminutive creatures is immune to all weapon damage. Reducing a swarm to 0 hit points or less causes it to break up ....

A swarm takes half again as much damage (+50%) from spells or effects that affect an area, such as splash weapons and many evocation spells.

~~~~

1: Weapon Damage Is any damage inflicted by a Frost Longsword halved? (That is, both the slashing part and the 1d6 cold part?) I admit, my party doesn't have one of those yet, but the answer has implications. And I'm bound to throw more swarms their way... so I'd really like to know if a weapon enchanted to add energy damage does any damage at all to a spider swarm, for instance.

The world seems to be a simpler place if "weapon damage" explicitly refers to bludgeoning, piercing, or slashing damage (and not energy damage). Then a Frost Longsword would indeed do only half of its total slashing damage but all of the 1d6 cold vs. a rat swarm, and 1d6 cold (only) vs. a spider swarm.

~~~~

2: AC The Rat Swarm listed in the Bestiary has an AC of "AC 14, touch 14, flat-footed 12 (+2 Dex, +2 size)." I'm incredulous! Shouldn't that be
... AC 10, touch 10, flat-footed 8 (+2 Dex, -2 size)?

Examples:
As it is, if my PC is throwing a splash weapon flask at a Large swarm, it can easily dodge! (Look, they're low level. This is a frikkin' CR 2 monster!) I just don't see how an entire army of rats, maddened enough to swarm, would effectively dodge a flung flask. Most of the specific rats would dodge the actual flask, sure. (One little rat might be done to death by the bottle the alchemist's fire is delivered in. Poor Short-tooth, we knew you well. No actual HP damage to the swarm, however.) But then the fire explodes, and envelops all of Short-tooth's short-sighted friends, who thought they were safe split-seconds earlier by simply moving one short inch to dodge the flask. That is, the swarm wouldn't dodge a thing.

With the AC that looks right to me, it's still tougher than hitting a tile on the floor, which has no Dex, and therefore an AC of 5. But if a PC tries to hit a tile on the floor, they have to go for a grid intersection. Oh, I know! They can go for the one in the middle of the swarm! No, the swarm still only takes 1 HP damage? Really? Times 50% more for... 1 total lousy point?

When we ended tonight, the party druid was up on a table, waving around a lit torch, smacking the rats coming at him. He's a gnome, so he's doing only 1d2 B +1 fire. But... it's an improvised weapon & he has a low STR, giving him at best a -2 to hit an AC of 14. Is it really that easy to miss the dozens of rats that are on the table with him? Again, I'd think -2 vs. AC 10 would reflect his dire straits quite well enough!

~~~~

3: AoE I touched on splash weapon attacks in my examples re: AC above. Let me summarize my current understanding, to be sure I have it right. If someone targets a swarm as a creature with a splash attack, and hits, it takes 150% of (typically) 1d6 damage. The attacker gets to specify which square of the creature they're aiming for, and anyone other than the swarm who is adjacent to that square takes 1 pt of splash damage. Since the swarm was the primary target, it takes no secondary damage. Similarly, if the attacker targets a grid intersection, the swarm can take no more than 1 pt of splash damage.

In terms of an AoE spell like Burning Hands, I suspect that the swarm again counts as only one target, no matter how many of its squares are affected, albeit for 150% of the damage rolled. However, I'm not so sure of myself here. Is this right?

~~~~

4: Dispersal What the bleep happens after they finally disperse these horrors? Apparently, hundreds of rats go streaming into the wall & floor cracks out from which they came. Can the swarm re-form later? Should it, given some time? Or is "break up" a different way of saying that the party has put an end to the threat for good?

~~~~

This is it for tonight, at least! Goodnight, and thank you for your help.


Rats swarms are made up of around 300 Rats moving all over one another, they have racial climb, and swim abilities that they can use as a unit. They do not need to maintain a 2x2 shape, they can twist to move through smaller spaces, but need to remain connected (I believe).

1: Weapon Damage: The weapon itself does 1/2 damage (if any), but applies all energy damage as normal, so a swarm immune to slashing, can still take 1d6 fire/frost damage from an enchanted sword.
The Gnomes torch should do full 1d2 fire energy damage to the swarm (not B).

2: AC: The tables modify the AC for swarms regardless of the originating creatures. There are also some legacy elements to some creatures, but 14AC for a rat swarm is not unreasonable.

3: AOE: Splash weapons will do 150% damage with no additional splash, any creature sharing their space WILL take the splash, so a cleric inside the swarm space, the swarm takes 1d6 (+50%), and the cleric takes 1dmg.

4: Dispersal: This is generally achieved when the majority are dead, 300 rats share 16hp (or more if you roll), so when they disperse it is because only a handful remain, their dense concentrations meaning many can be slain with a single strike. This equates to around 18 per HP point.

There is no reason one could not form up later, assuming there are many more rats in the area to bolster the numbers, a far more likely scenario would be individual rats, or things seeking dead rats as food.

5: Disease - Onset is 1d3 DAYS, this should not affect them for the battle itself, but it will suck later on. There are also the new Unchained disease rules
Unchained Diseases.
Which I like a lot more than the old ones for simplicity sake.

Rats are a great gateway Swarm, decent damage, still damagable by weapons, and it forces the party to use consumables/AOE spells before a more significant encounter.

Sovereign Court

Guardianlord wrote:
Rats swarms are made up of around 300 Rats moving all over one another, they have racial climb, and swim abilities that they can use as a unit. They do not need to maintain a 2x2 shape, they can twist to move through smaller spaces, but need to remain connected (I believe).

They do need to maintain a 2x2 shape, as in, they can't change into an L shape or a | or Z shape. So they can't snake out to attack PCs standing farther apart from each other. That used to be possible in 3.5 but not in Pathfinder. In Pathfinder all four squares of the swarm must remain adjacent to each other.

The 2x2 shape can be pressed together even tighter to move through narrow spaces however.


Ascalaphus wrote:
Guardianlord wrote:
Rats swarms are made up of around 300 Rats moving all over one another, they have racial climb, and swim abilities that they can use as a unit. They do not need to maintain a 2x2 shape, they can twist to move through smaller spaces, but need to remain connected (I believe).

They do need to maintain a 2x2 shape, as in, they can't change into an L shape or a | or Z shape. So they can't snake out to attack PCs standing farther apart from each other. That used to be possible in 3.5 but not in Pathfinder. In Pathfinder all four squares of the swarm must remain adjacent to each other.

The 2x2 shape can be pressed together even tighter to move through narrow spaces however.

Yes, sorry, that was a poor choice of words on my part. Essentially a Swarm can go anywhere the largest individual member of them can go. I guess this does technically mean a long, thin enough tunnel will be unusable by the swarm as they would not all fit in a tiny space longer than 10ft, which seems quite silly to me, they would simply move in a long line and regroup on the other side. I would personally rule that they can move in a non 2x2 shape to transition between spaces (Exclusively).

Sovereign Court

A swarm can get through a long thin tunnel, but they're not going to spread out into a 1x4 snake to do it. They'd be pressed together into a 1x2 bunch.

Just remember this and you'll be fine: all the spaces of the swarm remain adjacent to each other. If there's not enough room for the swarm, compress it to fewer squares.


Guardianlord wrote:

1: Weapon Damage: The weapon itself does 1/2 damage (if any), but applies all energy damage as normal, so a swarm immune to slashing, can still take 1d6 fire/frost damage from an enchanted sword.

The Gnomes torch should do full 1d2 fire energy damage to the swarm (not B).

2: AC: The tables modify the AC for swarms regardless of the originating creatures. There are also some legacy elements to some creatures, but 14AC for a rat swarm is not unreasonable.

Thanks for your explanation on the weapon damage vs. energy damage issue. And for confirming the AC, I suppose. But as for the torch...

Ultimate Equipment under Gear wrote:
If a torch is used in combat, treat it as a one-handed improvised weapon that deals bludgeoning damage equal to that of a gauntlet of its size, plus 1 point of fire damage.

Note that Core gives the same damage.

Guardianlord wrote:

3: AOE: Splash weapons will do 150% damage with no additional splash, any creature sharing their space WILL take the splash, so a cleric inside the swarm space, the swarm takes 1d6 (+50%), and the cleric takes 1dmg.

4: Dispersal: This is generally achieved when the majority are dead, 300 rats share 16hp (or more if you roll), so when they disperse it is because only a handful remain, their dense concentrations meaning many can be slain with a single strike. This equates to around 18 per HP point.

There is no reason one could not form up later, assuming there are many more rats in the area to bolster the numbers, a far more likely scenario would be individual rats, or things seeking dead rats as food.

OK, I hadn't paid attention to the possibility of a character being inside the same square as the swarm. But I hope you're not suggesting that the squares around the target one now get NO splash damage -- but just confirming that the swarm takes no additional damage.

As for dispersal, thank you for the idea of carrion eaters moving in! But yes, dispersal means putting an end to the threat -- wonderful.

Guardianlord wrote:

5: Disease - Onset is 1d3 DAYS, this should not affect them for the battle itself, but it will suck later on. There are also the new Unchained disease rules

Unchained Diseases.
Which I like a lot more than the old ones for simplicity sake.

Rats are a great gateway Swarm, decent damage, still damagable by weapons, and it forces the party to use consumables/AOE spells before a more significant encounter.

I will be certain to read those rules in a day or two! Thank you for pointing them out. And thanks for the reassurance that I didn't pull a stupid newbie GM trick by foisting the rats off on my party!

I quoted your lengthy, informative post in snippets for easier replies.
TL;DR: The only real question I had on your answers was in regard to the Small-size torch's damage -- 1d2 B +1 fire, or 1d2 fire.


I believe the other big question is on swarm movement.

Bestiary under Creature Types wrote:
A single swarm occupies a square (if it is made up of nonflying creatures) or a cube (of flying creatures) 10 feet on a side... A swarm can move through cracks or holes large enough for its component creatures.

I interpreted that as meaning that if my rat swarm has reason to move directly through a wall, it can do so as easily as the component rats could. (In a house riddled with rat-holes, very.)

I hadn't questioned what would happen if it had reason to flow down a 5-ft-wide hallway. So I'm making note: the answer is it gets more condensed, and occupies a "deeper" 5x10 space in the hall, until it reaches another room and can expand again to 10x10.


Torch and other flaming items would only do 1 point of fire damage to a swarm. You need area of effect attacks to fight a swarm. Single weapons will not do it.


swarm traits wrote:
The area occupied by a large swarm is completely shapeable, though the swarm usually remains in contiguous squares.

I've always allowed my swarms to L-shape or stretch out to e.g. 5'x20'. There is a reason you get swarm tokens in sets of 4 and on medium bases.

Sovereign Court

dragonhunterq wrote:
swarm traits wrote:
The area occupied by a large swarm is completely shapeable, though the swarm usually remains in contiguous squares.
I've always allowed my swarms to L-shape or stretch out to e.g. 5'x20'. There is a reason you get swarm tokens in sets of 4 and on medium bases.

You've overlooked a part of that rule:

Quote:

A single swarm occupies a square (if it is made up of nonflying creatures) or a cube (of flying creatures) 10 feet on a side, but its reach is 0 feet, like its component creatures.

Larger swarms are represented by multiples of single swarms. The area occupied by a large swarm is completely shapeable, though the swarm usually remains in contiguous squares.

A normal swarm occupies the same area as a large creature, but that doesn't make it a large creature.

A large swarm consists of a number of single-swarms. Each single-swarm is still 10x10. But if for example you have 4 single-swarms, they don't have to position in a 20x20 area, they could also position in a 10x40 area or an L or Z shape. Or even in a non-contiguous shape, but the large swarm prefers not to be disconnected.


Brother Fen wrote:
Torch and other flaming items would only do 1 point of fire damage to a swarm. You need area of effect attacks to fight a swarm. Single weapons will not do it.

Remember, this is a rat swarm...


I'd like to ask again, please: how much damage does my gnome's lit torch do to the rats swarming about him up there on the table? I'm assuming that Brother Fen's 1 pt of Fire was in reference to a spider-type swarm. So that means I've got the following possibilities on the table (so to speak):

1d2 B +1 fire
1d2 fire

Help???


Hitting A rat is not really relevant. Hitting enough of them at once to make a difference is the hard part. The small torch does 1d2 bludgeoning (-str penalty, if he has one) and 1 point of fire. And the bludgeoning is halved.

So assuming 10 str, he either deals 1 bludgeoning and 1 fire, if he rolls a 2, or 1 Non-lethal and 1 fire if he rolls a 1. (If penalties reduce an attacks damage to less than 1, the attack deals 1 nonlethal instead.)

And, interestingly, if it's nonlethal damage equals it's remaining hit points, it will disperse. But it will heal 3 nonlethal every hour, and once its nonlethal is no longer greater than it's hit points, it will reform.

Edit: Oops, my bad. Half from slashing and piercing damage. Bludgeoning does full. Point about nonlethal still stands though, should someone else hit them for less than 1.


Thank you, toastedamphibian: 1d2 B + 1 fire. As for slashing/piercing risking non-lethal, it's something chilling to keep in mind...


I just have to post the update. When informed of the possibly chilling consequences of nonlethal damage to a swarm, but the minimal damage his torch was inflicting, the gnome promptly used his Weather domain power, Storm Burst, and scored 6 nonlethal. Ack! I thought. But I dutifully recorded it, and went on. A round passed, and the swarm was down to 1 HP, and the 6 nonlethal (or 7 HP, but with 6 nonlethal against them, if that's clearer). And the hunter's tiger attacked. And critted. We use Crit cards, and she did 15 HP damage in one attack!

Gore Alert:
Given the card the player drew, I ruled that the tiger damaged (but didn't break) the door (!) as she came through it, and then raced through the swarm, swatting rats aside as she went. (Normally, she'd have taken only a 5-foot step, but when I looked at how much mayhem she was causing, she had to be rampaging.) She knocked rats onto the ceiling, where they stuck and dripped blood. She flung rats into the farthest corner of the room. The walls were running red with rat blood. My swarm had more than the standard HP, but that still was over half of its max -- certainly, well over the 7 HP remaining. I told the players that a bare handful of rats dived into cracks and crannies, but that any other swarms they might meet in this house of evil would be wholly composed of new rats.

(In fact, more than one swarm per dungeon seems anti-climactic.)


Quote:
A swarm has no clear front or back and no discernible anatomy, so it is not subject to critical hits or flanking.


A swarm of rats is not particularly nasty. I sent like 3 at my lvl 2 party, and they moped them up with limited damage (I had reskinned them as bunnies and removed filth fever, but I don't think keeping it would have changed much).


Matthew Downie wrote:
Quote:
A swarm has no clear front or back and no discernible anatomy, so it is not subject to critical hits or flanking.

OOOOPS! Oh, well, it made for such a good story! I'm not going to retcon it. That's a slap on my wrist, though.


Goblin_Priest wrote:
A swarm of rats is not particularly nasty. I sent like 3 at my lvl 2 party, and they moped them up with limited damage (I had reskinned them as bunnies and removed filth fever, but I don't think keeping it would have changed much).

Three swarms of killer bunnies???? Basically, 1,000 of them???? All at once????

Where?


With a 15' move speed the party could have, literally, walked away. This is the most frequently chosen option for my groups.

or

A single character with alchemist fire or AoEs could have attacked and walked out of range of retaliation each round.

Taking losses from a single rat swarm, at any level, is a result of poor tactics. Nothing more, nothing less. The only time a swarm like this should pose a threat is if the party is in a small, enclosed area or their movement is otherwise restricted.


Snowlilly, OK, maybe they were bull-headed. But they wanted to get into a house to (hopefully) rescue innocents -- so far, sadly, they've just found body parts. The front porch & front door were both seriously trapped specifically because the inhabitants didn't use them. And the windows were all boarded up. So when the hunter looked for tracks at the side door, I had to say she found quite a few, too indistinct to analyze. At that point, the party correctly deduced the situation, and decided to enter through the kitchen. Unfortunately, the two doors from the kitchen into the house were locked, and I've extended the time that it takes to pick a lock.

I suppose that they should have exited the house and lobbed AoE's in through the open door and the kitchen window -- which they had broken out. The swarm would have left to follow them, sure, but then it's just a matter of move, lob, and stay ahead. For those characters who had AoE or bludgeoning capability. But at least they'd have been able to stick to relatively open areas... Well, as open as a narrow path through woods would be... Or an overgrown & badly tended truck farm... (I was certainly assuming that the fields would be difficult terrain.) And rats wouldn't be vulnerable to the gnomish druid's favorite outdoor trick, Entangle...

As it is, they {all stayed in the kitchen and} took enough damage to eat up some healing capabilities. And two characters will be dealing with illness over the next few days. Did they err in strategy?


One thing I've noticed some GMs overlook is that Swarms (most) are mindless and easy to 'distract'.

They almost always go after those that are closest, so if someone is hurt, you can stick someone else in front of them to 'protect' them. Have ping ponged a swarm before by using this tactic.

...or you can try something different. In the case of the rats, might be able to 'distract' them by tossing food down in another square and running away.
This tactic does depend on the GM if it works or not.

Scarab Sages

bitter lily wrote:
Thank you, toastedamphibian: 1d2 B + 1 fire.

Just an extra note, the weapon is "One handed" which means it can be wielded in a single hand, your "off hand", or in two hands. So the small torch deals 1d2 B + STR Mod (0.5x, 1x, or 1.5x) + 1 fire damage. Doesn't matter if they have 10 or less strength, but they can deal decent damage if their strength is high.


dragonhunterq wrote:
I've always allowed my swarms to L-shape

SWARM TETRIS!!! Every time you shape a swarm like that and do not have the tetris theme running, you're committing a crime, you know that?

The Exchange

Derklord wrote:
dragonhunterq wrote:
I've always allowed my swarms to L-shape
SWARM TETRIS!!! Every time you shape a swarm like that and do not have the tetris theme running, you're committing a crime, you know that?

getting a little serious on the "shapeable" part of a swarm -

From the PRD:

Swarm Subtype: A swarm is a collection of Fine, Diminutive, or Tiny creatures that acts as a single creature. A swarm has the characteristics of its type, except as noted here. A swarm has a single pool of Hit Dice and hit points, a single initiative modifier, a single speed, and a single Armor Class. A swarm makes saving throws as a single creature. A single swarm occupies a square (if it is made up of nonflying creatures) or a cube (of flying creatures) 10 feet on a side, but its reach is 0 feet, like its component creatures. In order to attack, it moves into an opponent's space, which provokes an attack of opportunity. It can occupy the same space as a creature of any size, since it crawls all over its prey. A swarm can move through squares occupied by enemies and vice versa without impediment, although the swarm provokes an attack of opportunity if it does so. A swarm can move through cracks or holes large enough for its component creatures.

A swarm of Tiny creatures consists of 300 nonflying creatures or 1,000 flying creatures. A swarm of Diminutive creatures consists of 1,500 nonflying creatures or 5,000 flying creatures. A swarm of Fine creatures consists of 10,000 creatures, whether they are flying or not. Swarms of nonflying creatures include many more creatures than could normally fit in a 10-foot square based on their normal space, because creatures in a swarm are packed tightly together and generally crawl over each other and their prey when moving or attacking. Larger swarms are represented by multiples of single swarms. The area occupied by a large swarm is completely shapeable, though the swarm usually remains in contiguous squares.

SO>>>

"Larger swarms are represented by multiples of single swarms..." these larger swarms (composed of multiple single swarms - each of which "...occupies a square ...or a cube ...10 feet on a side,"... ) ... are "completely shapeable, though the swarm usually remains in contiguous squares".

If a single swarm is shapeable, (able to form in an L shape) then it would follow that it would not have to remain in contiguous squares. Meaning, if we can shape it into a line four (5') squares long - then we could brake those squares up and move them in NON-contiguous squares.

Please let's not start down that path...

It is only when we take the line of the description of swarm "... The area occupied by a large swarm is completely shapeable, though the swarm usually remains in contiguous squares...." out of context - (and ignore the word "usually") ... that we can assume that a single swarm is shapeable...

If taken with the line just before it in the paragraph ...
"Larger swarms are represented by multiples of single swarms. The area occupied by a large swarm ..." ...
we will see that the area occupied by multiple single swarms (i.e. a large swarm).. is completely shapeable...


Murdock Mudeater wrote:
bitter lily wrote:
Thank you, toastedamphibian: 1d2 B + 1 fire.
Just an extra note, the weapon is "One handed" which means it can be wielded in a single hand, your "off hand", or in two hands. So the small torch deals 1d2 B + STR Mod (0.5x, 1x, or 1.5x) + 1 fire damage. Doesn't matter if they have 10 or less strength, but they can deal decent damage if their strength is high.

Strength 10 for the gnome, sadly. Thanks!

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