Hiveminds...

[Aminar]

I'm working on a concept for a DF session using Never Never based entities with the following criteria.
They are a hivemind.  For every Ten of them linked they are about as smart as a human being.
They are about six inches tall.  They are bipedal, and capable of using tools, but have chitinous skin.
Necessary powers.
Diminutive Size. -1
Inhuman Toughness.  -2(Gives them 4-5 Physical Stress, 1 Armor total always with diminutive size.)(In Fatecore this would just be Chitinous Endoskeleton -1.  Gain Armor 1)
Then the following long and complicated power.
Hivemind -1  This power may be taken multiple times.  For every 1 point spent the hive grows by ten.
Abilities included-
Multitasking-The Hive may perform any number of skill checks at a given time outside of combat up to the number of Hive members.  For every 2 Hive Members below 10 performing a task take -1 on the roll.(So a lone Hive member will take -4 on any task.)
Focus- For every ten Hive Members focused on a task add +1 to the roll.  Hive members focusing on a task being performed by another body may not take any actions of their own.
-Mental Link-  The Hive takes all mental stress as one.  Each member of the hive takes physical stress separately.  Whenever a member of the hive is taken out the Hive takes 2 mental stress.
-Mental Range-The Link has a radius of 1 mile from each body to the next.

Because the Hive is a never never entity, and not a faerie they cannot take magical abilities(Or really much of anything not directly above except for a few things.
I'm torn on the balance here.  I mean, on one hand, a player using this could take up the whole session just doing their own awful rolls.  Or they can focus everything together and gain some insane bonuses.  At the same time, in a physical fight they are severely handicapped by lack of feasible damage output and the fact that anyone finding their cowering pile of extra brainpower can take them out in just a few rounds.
Thoughts.

I'm actually hoping to balance these for Fatecore starting characters as well, given that I'm using them in Dresden to test them for another project that will be in fatecore.

[Taran]

First:
I'd give them pack instincts

Second:
I'd make the "hive" one entity.  The number of creatures would increase their stress track and their skill pyramid(to represent how they are smarter/tougher/and able to do more) as well as their total refresh(to buy stunts etc..to represent their increased deadliness or usefulness).  They'd take consequences like: mild - "disorganized group"  moderate - Swath of dead creatures;  Severe: etc..

 - The more creatures there are, the higher their skill pyramid.  This represents how quickly they can get a job done.
*Let's say there is 2 creature building a boat (difficulty 5 - 1hr time increment).  Give them a crafsmanship of 2.  On a good roll they'd finish it in an hour, but it's likely to take longer.
* Now, let's say there's 20.  Give them a craftsmanship of 5.  On an average roll, they'd finish the boat in 1 hour, but on a good roll, they'd finish it much quicker because extra shifts would go into reducing the amount of time it takes to do a task.

Third
To represent more numbers:
As they increase in number, give them powers that lets the creature have an ability to attack a zone.
Give them a stunt that lets them do melee attacks as a spray attack. 
Give them a stunt to give a bonus to spray attacks, so that they're somewhat effective with it.  Maybe make the stunt reliant on the number of creatures.  Every multiple of 10 = +1 to hit for spray attacks. (maybe capped by their weapon score or something or make it multiples of 20...dunno)

[Aminar]

I don't want to modify them too far from how a typical PC operates.  I could make the hive one entity for physical stress, but that limits the ability to split the hive into multiple parts, or at least the realism of it in certain respects, and makes them very unintuitive to play.  I want this one PC legal and easy.

If Player 3 is a Hivemind, with 20 Hive members he might be most effective in combat hiding 19 of his bodies and then leaving them to focus so he can perform all tasks at +2.  I want him to be able to do that, but if the Hive is all one entity for physical stress he's not able to adapt like that.(In short it doesn't fit the way the hivemind is designed, as if each member is more processing power for the whole entity.

[Taran]

If it's for a PC, why not just use true shapeshifting and modular abilities?

True Shapeshifting would give him a skill flip depending on the size/shape/quanity of creatures.  So if he's hiding, and everyone is concentrating on stealth, stealth would be the apex skill.
His mental faculties of the Hive would be represented by the fact that mental skills are limited in how they can be changed.

Modular abilities would give him powers based along the same lines.  If there's one hiding and spying, he gets diminuitive form and cloak of shadows, if it's 20, he gets toughness.

I don't know how you'd give one PC multiple physical stress tracks while making it legal.  The physical stress track can just represent multiple creatures dying/going unconcious or, if there's only one creature present, the stress track represents the stress of that particular creature.  The modular abilities will dictate whether that one creature is easy to take out(low endurance, diminuitive size, no toughness powers) vs trying multiple creatures which would be tougher(toughness, High endurance,).

[Aminar]

Yeah...  I tried to balance the multiple stress tracks as best possible.  Mainly by making them useless offensively in physical combat, limiting the impact of endurance on tanking ability, and making defending the whole Hive at once nearly impossible.
Largely the issue is that the creatures were designed from a story perspective and getting them to function as they do in story, in game is a difficult task. 
I think maybe by making every refresh after the first five Hive members, and dealing half of all physical stress as mental it could work...
So a hit for 4 physical stress to any member of the hive would deal (4-1)/2=1.5 rounded down to 1 mental stress.  A 10 stress hit to a member of the hive would deal 4 mental stress +2 if the hive member were taken out... 

I don't really like the true shapeshifting/modular powers aspect.  It could be made to work, but by and large the PC would be better spent taking a different concept with the same powers, they wouldn't have to work so hard to justfy what they wanted to do or limit themselves so much.(Also too much refresh for fatecore...)

I can see where Pack instincts fit in as well, but the power already largely covers it, and I'm trying to keep minimum char refresh to 3...  Which is actually still too many for fatecore in some ways, but I'm willing to stretch things to stunts.(noting that at 3 refresh there isn't really much the character is capable of other than doing a bunch of things at the same time badly.

[Sanctaphrax]

I don't understand this Power. I've read it, but I have trouble following the write-up.

Let me start with a very basic question. Is the hive one character with a Power that gives it a bunch of bodies or a bunch of characters that each have a Power that lets them share a single mind?

[Aminar]

1 Character.  Bunch of bodies.  One Mind.  That mind gets more powerful as more brains are connected to it.

[Sanctaphrax]

More simple questions.

1. Does this Power provide multiple actions in a conflict?
2. What does focusing on a task entail? If someone with this Power has one body looking for a clue at a murder scene and nine bodies safe in a basement a few hundred metres away, can they have all of their bodies focus on finding the clue?
3. How does this Power affect social stress?
4. What rolls does this Power affect? Does it boost/penalize social actions based on number of bodies? How about Resources rolls? How about defence rolls?

[Aminar]

1.  Most likely yes, but with the above restrictions about negatives to doing multiple actions at once with less than ten minds mentally involved.  So you could split ten minds into two groups of five and take some negatives to do two actions at once.
2.  All the bodies mental power would be focused into finding the clue, leaving the distanced bodies, the ones not searching, effectively comatose and unable to act.  On the other hand they could all be there working on the task and function basically the same.
3.  I have never used social stress, I find it cumbersome.  Fate Core agrees with me.
4.  It affects physical and mental actions.  It would not affect social rolls, nor resource, nor contacts as those are a function of what the individual identity owns and knows, not the bodies of the hive.  One mind-enhanced by number/amount of connected brainmatter-multiple bodies.

[Sanctaphrax]

Pretty sure it's too good, then.

Each Refresh spent is worth 10 bodies. 10 bodies is worth a full extra action. 1 Refresh to act an extra time each exchange is crazy good.

Plus the skill bonus could be very powerful if used intelligently.

And since it apparently doesn't penalize social rolls, you can have all of your many bodies out in the world chatting up people with your full skill.

Yeah. Definitely too good.

[Aminar]

The lack of focus does penalize social rolls, it penalizes all actions because of insufficient cognitive ability.  The way this works a single body has an IQ of around 10.  Oops.

I've cut down the number of extra bodies to 5 per refresh after the first, not sure that's good enough, but anymore and it starts being not worth it/the numbers add up oddly unless I go to 2.  As another note, remember that many of those actions are pre-gimped by tiny size, one of the requirements of using the template that can use this power.  But that comes with advantages too.  It just limits their use in combat situations.

[Sanctaphrax]

If Diminutive Size is meant to be required for every hive mind, then it should probably be an explicit Must.

Cutting down on the number of bodies helps, but the Power still has some weird interactions. For example, it lets you have 29 bodies hiding in a bunker, concentrating on the action of 3 bodies to make those bodies badass fighters. Then if someone takes down a body, you can send in another one.

I have another idea for handling this. It's based on your idea, but it goes a little farther.

HIVE MIND [-2]
Description: You are not a single entity. You have one mind, and many bodies.
Skills Affected: Many.
Effects:
Ten Bodies. You have ten bodies. You may divide them into groups however you like. Each group is considered a single character, and receives a single action in a conflict. If there are less than 10 bodies in a group, that group takes a -1 penalty to all physical or social rolls for each 2 members missing from it. Knowledge rolls, Resources rolls, and Contacts rolls are unaffected by this...you can only take a normal number of them, but they're not penalized.
Altered Stress Tracks. Each group has its own physical stress track, but you only have one mental stress track total. Social stress should be handled on a case-by-case basis by the GM. You have only one set of consequences. For every three bodies in a group, that group gets a point of stacking physical armour against single-target attacks. Groups fight at full effectiveness until taken out, even if you decide to narrate a consequence as having a group member knocked out or something like that. When combining  or dividing groups, the resulting groups have as much stress as every group that they got members from put together. If this would take it out, you can't create that group.
Mental Link. If one of your bodies is more than a mile away from all of your other bodies, it falls unconscious.

It's far from perfect, but it's something.

Dunno how exactly to handle more bodies.

I considered adding some kind of bonus physical consequence where you sacrifice bodies to absorb stress, but I couldn't think of a good way to handle it. I still think it's a good idea, I just don't know exactly how to go about it.

[Aminar]

Diminutive size is a must.  I'll note that for my players, although they already know given it's only allowed for a single template.

I'm not sure how to mitigate the multiple actions, although I think maybe some verbage on how multiple actions works when in surplus. A penalty for taking multiple actions is out of flavor given that the template is designed to represent tiny engineers who use their enhanced brainpower, tiny size, and ability to take multiple actions to make amazing tech.  Giving an action cap doesn't really fit either.
Granted in the explanation you gave, with 27 Bodies sitting back and 3 fighting you could have
1 Fighting at +2 and the others fighting normal or 2 Fighting at +1 and 1 at normal.  It leaves seven bodies doing nothing.  That's still functionally a little broken.  Even with a Damage cap of 6 and 4 refresh spent to get there.  Or is it?  I mean a wizard can do that with an AOE spell for about the same and have different limitations.(1 mental stress.  Hit allies in the zone.  Can hit more than 3 and does full damage to everything.)  Thoughts on this versus AOE in combat? 

[Sanctaphrax]

Multiple actions are much better than zone attacks. Zone attacks just do stress, multiple actions can do anything.

[Taran]

Make it spray attacks unless the whole unit is focusing on one enemy.  It makes sense.  The less they co-ordinate, the less threatening they are.

They break into 3 groups: 1 in zone 1, one in zone 2 and one in zone 3.  Sure, they're attacking three different enemies in three zones, but their attacks are less potent than if they all gather in one zone and attack one enemy.

In fact, you may be able to use spray attacks for other situations, such as social situations if the unit is not working as a team.

And really, could represent any activity they do with spray attacks.

If they're concentrating on building a boat they roll their craftsmanship at full
If they're building two boats, they roll craftsmanship using spray attack rules and dividing the result between the two groups
If they're doing two different activities at once, use the higher skill but have the lower skill modify it down.  Then roll and divide.