How does it work when swarms or mobs take stress in Fate Core or Accelerated?

Question

Let's say we have a group of four crabs in Core or Accelerated, but I'm treating them as a mob.

One individual crab looks like this:

Crab

Stress: [] (one stress box, further damage takes them out)

First things first, here's my understanding of such a monster. They can take 1 stress, which leaves them open for a blow which would take them out. So a weak, 1-stress hit wouldn't take them out, but a 2-stress hit would. Ok.

Here we have the swarm of four crabs:

Crab Swarm (four)

Stress: [] [] [] []

For the purposes of this question, it matters how many crabs are still alive - maybe each crab gives a bonus or something.

My questions are these:

1. What happens if the swarm takes 1 stress? Does a crab die or does it just lose its "stress shield"? What would happen on the next 1-stress hit? Does it get taken out and the second crab get wounded? Or does that first one just get taken out? Would that mean the swarm has 8 effective stress?
2. What happens if the swarm takes a blow of 4 stress? Is it defeated? Does it get to choose if it leaves all crabs open for defeat? Do all but one die out? Does it have 4,5 or 8 effective stress?
3. How is the game changed if each crab had multiple boxes of stress, or one box of 5 stress? Does the swarm then have 20, 21 (5 x 4, plus 1 swarm takedown stress) or 24 (5 each, plus 1 final blow) effective stress?

I am interested in answers that relate to both Fate Accelerated and Fate Core.

Answer 1

The manner in which individual mooks' stress boxes add up in a mob differs between Core and Accelerated.

In Core:

When a mob takes a hit, shifts in excess of what’s needed to take out one NPC are applied to the next NPCs in the mob, one at a time.
...
On Lenny’s turn, Landon deals two shifts to the mob he’s facing, enough to take out two thugs and reducing it from a mob of three to a single nameless NPC.

The thugs in the example are "average" NPCs with no stress boxes individually, so each one "absorbs" one shift and is taken out. A three-shift hit would take out the mob all at once.

In your example mob of four crabs with one stress box each, you would indeed need a total of eight shifts to take out all four crabs, since each crab is taken out after every two shifts. A two-shift hit would take out a crab right away; a three-shift hit would take out one crab with two of those shifts, then the third shift overflows to a second crab, and so on. Note that a crab that's taken out isn't necessarily "dying" or "dead", just that it can no longer contribute in the conflict.

In Accelerated (scroll down about two pages):

Groups of Mooks: If you have a lot of low-level bad guys facing the PCs, you can make your job easier by treating them as a group—or maybe a few groups. Instead of tracking a dozen bad guys, you track three groups of four bad guys each. Each of these groups acts like a single character and has a set of stats just like a single mook would:
...
Give them one stress box for every two individuals in the group.

This seems to overwrite the usual rules of assigning 0-2 stress boxes to individual mooks and instead calculates stress based on total numbers. So your swarm of four crabs gets two stress boxes. But since the mob is treated as a single character, the first box absorbs one shift and the second absorbs two. So a pair of one-shift hits or a one-shift hit and a two-shift hit in either order would fill the boxes (in the former case, it's because you can't "partially fill" a stress box), and the next hit would take out the mob. A three-shift or greater hit would take it out immediately since characters can check only one stress box per hit, and neither box is big enough to absorb that many shifts (as this answer reminded me). Plus, mooks in Accelerated can't take consequences by default.

Answer 2

Stress is neither damage nor a representation of the numbers in a mob. It is an abstract measure of how much narrative effort you must put into getting your way with your opponent.

In another perspective, it is similar to the numeric difficulty of defeating an opponent, only that you can work towards that instead of having to roll at once. You can defeat a 3-box mob by rolling a +4 or rolling two +3's in succession.

How that translates into the narrative is entirely your prerogative but keep in mind that stress is something that goes away at the end of the conflict. So I wouldn't suggest using it to imply dwindling numbers (unless those numbers are easily replaced). It's more like temporary stuff that happens, like coming under concentrated fire, freaking out, getting divided etc.

An example would be an angry street mob of peaceful protesters that would withstand a lot of abuse but disperse at the first sign of lethal violence. Taking them out could mean just roughing up one of them and the rest flee, dismayed by the impunity of their aggressors.

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That being said, if you still want to associate stress boxes with numbers in a mob, let me say first that there is no official rule for that to the best of my knowledge. But the math behind the game mechanics implies that a n-box threat takes twice the effort to defeat as a (n-1)-box threat, so you could take it as every additional stress box in a mob represents a doubling of the numbers.

If your single crab has a single stress box, then a 2-box mob of them has two crabs, a 3-box mob has four crabs, a 4-box mob has eight crabs and so on.

In such a case, filling a mob's highest stress box could mean effectively halving their numbers