Faction Ability:
Berserk – You may spend one command action to mark a unit with berserk. The unit gets (+1)+0/+1, –1/-0 and courage +1. Change the unit's orders to close with no modifiers. You may not change the unit's standing orders or take direct control of it until berserk is removed. All bonuses or negative effects only last while engaged. This lasts until the unit routs or does not do a single point of damage during a round of combat.
NOTE: If the unit does not have defensive skill, it takes one point of damage.
I'd have to play this to see how it was. My gut feeling is the "erase if it does no damage" is going to be really annoying because half the time it is a kick in the nuts when something you already hate happens (guy does no damage) and the other half of the time you'll be wishing you could use defense cards on your own attacks because you want to get rid of the thing! I dunno quite what to do about it though; perhaps it is just the price of barbarism and the reason I'd command good Greek troops any day

Persistent – Units that are persistent never rout, but if they fail a rout check, they lose one defensive skill. If there is no defensive skill to subtract, they take one point of damage.
Vengeful - If a unit with vengeful is in the yellow or red, it does not suffer any penalties but it gets C+1 while in the yellow and C+2 when in the red. Note: They still have to take rout checks.
I think Persistent is the core of an interesting idea, but there are two issues with it, in my mind.
-It doesn't play particularly well with the faction ability because you care less if it routs so the +1 C matters less, and you're quickly going to zero out the defensive skill which means your guys are just going to be taking damage left and right.
-Tracking decreasing defensive skill is a pain in the butt. I don't mind it on the faction ability because you've got a box to remind you, but with this one it is going to lead to lots of marks on cards and annoyances. I already forget blessings half the time.
There's also the additional issue that Battleground factions aren't novels; they're short stories. You don't need three major abilities for a faction of 13 units. Look at the existing ones; they have one command action ability and maybe another one. (A few have a major one and a few rarely used minor ones, like Dwarves or High Elves.) I think I'd be tempted to keep vengeful and move persistent to a different kind of faction, maybe summoned creatures of some sort or some kind of undead.
Core units:
Savages: Offense: (5) 4/6 Defense: 0/2 Range:- Courage: 12 MC: 3.5" Health: 4-2-4
Persistent.
Equipment: Axes, clubs, leather armor.
Mercy? Dream on, fools!
Why are these guys 0/2? Humans tend to be 1/1 when in leather with no shields. I'd give them "thick hide" armor to justify 2 toughness, and make them 1/2 so they go to 0/2 when berserk.
If you're giving a unit a faction ability that represents it becoming careless with defense in order to go into a frenzy, you don't need to give them a lower defense due to carelessness with their defense; the faction ability does that for you!
I also assume they dual wielding the clubs and axes; if that's the case, they should probably be (7) 4/5; see Dwarven Hammermen and Orc Marauders. Normal units with dual wield weapons have 7 dice. (5) 4/6 would be a good profile for an unskilled (hence 4 skill) guy with a great weapon.
Barbarians: Offense: (5) 5/6 Defense: 0/3 Range:- Courage: 12 MC: 3.5” Health: 3-4-4
Vengeful.
Equipment: Leather armor, battleaxe, mace.
"YEARRRGHHH!!"
Estimated Cost: Around 200 points
These guys have the same armor as their fellows but somehow gained a mysterious point of toughness. Is it just that they are super hardy? In any case, I suggest giving them 1 base defense skill as well. If nothing else, the whole army is going to get shot to pieces if they don't have that.
Their armament also doesn't make sense to me. Again, dual wield on a normal sized unit means 7 dice, and 5 dice + 6 strength usually means two handed weapons. You could justify +1 strength if they are just that badass, but if you want them with two weapons, give them 7 dice.
Bandits: Offense: (6) 5/5 Defense: 1*/3 Range:- Courage: 12 MC: 5” Health: 3-4-4
Vengeful.
+1/+0 vs range.
Equipment: Dark leather armor, spiked clubs, spears, maces, etc.
These dodgy bandits are experienced in the art of dodging arrows.
Estimated Cost: Around 220 points
Seem fine, though why do they have 6 dice? Are there more of them than a normal unit? 6 is a pretty odd number; usually cavalry and spearmen get it and not much of anyone else.
Axe Hurlers: Offense: (5) 4*/5* Defense: 1*/2 Range: 7" Courage: 12 MC: 3.5” Health: 3-3-4
Vengeful.
(+0) +1/+1 and +1/+0 when engaged.
No penalty for move and shoot.
Equipment: Leather armor, shield, hand axe, throwing axes.
Getting executed is bad enough, but when you get executed from afar...
Estimated cost: Around 240 points
I like this unit, but I'd give them 5 skill; 4 skill on a range unit is really pretty crippling due to all the accuracy modifiers. I also once again am not sure why they're getting +1 strength in melee given they aren't using two handers; why is a hand axe str 6 when throwing a similarly sized axe isn't?
In Battleground units, less is more. You can tell a very detailed story just with the numbers, so in a lot of factions you're going to have a lot of units that don't have many or any special rules. Based on the language of the game, though, I'm not understanding the stories most of your units are telling. This isn't to say they're wrong per se, just that I think you need to come up with a justification for why they vary from baseline in these ways and with a way of making that justification clear to the player.
Maulers: Offense: (5) 5/7 Defense: 0/3 Range:- Courage: 12 MC: 3.5” Health: 3-4-4
No charge bonuses.
Equipment: Leather armor and maul.
These mauls can really maul people- why are they called mauls then?
Estimated Cost: Around 260 points
Why don't they get a charge bonus? I also still really don't like the 0 defense thing. It really is quite a bad drawback and it makes your faction ability less interesting because it is less often going to be an interesting choice (-1 defense is going to translate into way more than a point of damage pretty fast.) It can also be intensely annoying to play against, especially when you have a big high/low contrast like that, because some command cards are garbage whereas others are worth their weight in gold. Having factions have a "better" defense stat is nice because it varies unit values, but generally those are only +1 over the "bad" stat (2/3 or 3/2) or at best +2 (Ravenwood.) +3 is a huge variance and means a lot of games will vary a lot based on if people draw Might/Force or if they draw Accuracy. That's not so cool IMO.
Fishermen: Offense: (5) 4/4 Defense: 1/1 Range: 3.5” Courage: 10 MC: 3.5” Health: 3-2-3
May not be given berserk.
Equipment: Leather armor, fishing rods improvised as whips, harpoons.
Even the fishermen are forced to take part in wars.
Estimated Cost: Around 90 points
This is a fine chaff unit. I think it'd be closer to 80 points but that's nitpicky

Compare to Brownies; +2 health, but -3 courage. Seems like they should be pretty similar in cost, these guys should maybe even be a bit cheaper.
Standard units:
Druids: Offense: (4) 4/3 Defense: 1/1 Range:- Courage: 13 MC: 3.5" Health: 3-2-1
May not be given berserk.
Prediction. During your movement and command phase, if you have a unit of druids, you may look at the top 3 cards of your opponent's command card deck. You may spend a command action to put one command card at the bottom of the deck. You may also choose to spend 2 command actions to shuffle his deck.
Fog of mystery. While a unit within 7" range of the druids is being attacked, you may change one of the opponent's die into a "5". You may only use this ability on a unit once per turn per unit. Using this ability counts as playing a command card.
Equipment: Hood, robe, staff.
Estimated Cost: Around 130 points.
I like these guys overall. The command card ability is wordy, but pretty neat.
Flailers: Offense: (6) 6/6 Defense: 2*/2 Range:- Courage: 13 MC: 3.5” Health: 3-3-6
Vengeful.
Fearsome.
No other unit may engage a unit engaged with flailers, but flailers can pinch.
-1/-0 when being pinched or pinching.
The friendly unit(s) that is/are engaged with the same unit as the flailers gets C-1.
Equipment: Flail, shield, chainmail armor.
No one dares to interfere with these fearsome fighters.
Estimated cost: Around 320 points
Huh. That's pretty cool. They definitely know what they want to do!
Hunters: Offense: (6*) 5*/5* Defense: 3*/0 Range: 3.5" Courage: 12 MC: 5" Health: 3-4-4
Vengeful.
(-1) -0/-0 when charging.
(+0) +1/+0 vs cavalry/large units.
(+0) +0/+2 when holding vs charging cavalry/large units.
+1/+0 vs range.
Javelin rules. Free attack before engaging unless final rushed on the flank/rear or gets pinched.
Equipment: Javelins, spear, leather armor.
These ruthless and savage hunters fear no beast.
Again, why do they have 0 toughness in leather armor when other units in the army have 2 or even 3?
Zealots: Offense: (7*) 5/6 Defense: 1*/3* Range:- Courage: 14 MC: 5" Health: 6-2-2
Persistent.
Fearsome.
Passes all fear checks.
+0/+1 vs range.
Permanently on close and may not be given other standing order modifiers or directly controlled. When assigning standing orders, an objective unit must be given.
(-1) -0/-0 and -1/-0
Equipment: Spiked flails, spiked maces, battleaxes, spiked clubs, etc.
Zealots have been fighting years for an unknown cause which spurs them on.
Estimated cost: Around 280 points
I like them. Not sure why they get the +1 toughness against range, though. Also, what does the "(-1) -0/-0 and -1/-0" at the end mean?
Elite units:
Gnasher Cavalry: Offense: (6) 5*/7 Defense: 1/3* Range:- Courage: 14 MC: 5" Health: 4-2-2
Persistent.
Cavalry.
Fearsome.
(+0) +1/+0 and +0/+1 when charging (this is in addition to the normal charging bonuses).
Always has 1 impact hit, even when charging.
Equipment: Battleaxes, maces, warhammers, chainmail armor.
Gnashers are huge creatures with incredibly strong jaws. They are infamous for their uncontrollable temper.
Estimated cost: Around 370 points
What does the "always has an impact hit" mean? Normally you only get impact hits when charging. Also, why do they have reversed charge bonuses from every other cavalry?
Berserkers: Offense: (7) 5/7 Defense: 0/3 Range:- Courage: 14 MC: 3.5” Health: 5-2-5
Persistent.
Vengeful.
Fearsome.
Permanently on close and may not be given a standing order modifer or directly controlled.
Equipment: Battleaxes, spiked maces and leather armor.
Barabarians are brutal, zealots are vicious, executors are deadly, but berserkers are all three.
Estimated cost: Around 350 points
Those are still really brutal attack stats for a human-size thing. They apparently use two one-handed weapons and hit as hard as Ancients or Trolls! I'm not sure how that works; 6 is already pushing it hard for a dual wielder.
I also feel like you need to be really careful about uncontrollable units if you want to keep that faction ability. These guys are already berserk; what does marking a box on them to make them even more berserk mean? Between not losing a defense skill and already being marked on close, it basically gives them free (+1) +0/+1 and C +1. Aside from that being broken, it isn't an interesting choice anymore because they get very little downside from it. This is especially true because they have a billion green health and don't care about being in the yellow or red anyway.
I don't think every Battleground faction is perfect about making command actions a choice (I'll pretty much always mark Hawk Bravery or Lizardman Fury on everyone who might take and survive a hit, for example) but when you have an ability that good, balanced by some strong downsides, I don't believe it is very wise to make the faction such that those downsides don't apply fully to all the units.
Chieftains: Offense: (6) 6/6 Defense: 2/3 Range:- Courage: 14 MC 3.5” Health: 5-3-4
Vengeful.
Persistent.
Equipment: Chainmail armor, bludgeons, battleaxes and shield.
Only elite berserkers or gnasher riders may take on the role of a chieftain.
Estimated cost: Around 440 points
This is a fine elite unit, though again I'm not sure where that exact dice number came from.
Command Cards:
Ruthless Fury x2: Play during an attack, before you roll to hit. A unit with berserk gets (+0) +1/+0 and negates the first point of damage in combat. Otherwise, it only gets (+0) +1/+0.
I think you meant (+1) +1/+0 for the first ability. Also, I think this card is probably a little bit too good. Though I do kinda like the design space of a red card that gives a minor defense boost, my issue is that that's not a minor defense boost, it is a very strong one that stacks with a blue card. I think at the very least you should make it only work if you haven't played a defense card.
This card also feels very artificial to me because if it is the opponent's turn, you can't get the defensive benefit (since the unit has already been attacked by the time you can play the card.) I think you make it a hybrid red/blue card that gives both benefits, but stops you from playing another card on either attack or defense, though even then the fact that "prevent one damage" is always so reliably useful makes it a very strong card.
Resilience x2: Play during an attack, before your opponent rolls to hit. The unit gets +1/+1 if the enemy is using ranged fire. Otherwise, it gets +0/+1
I'd say "before the opponent rolls to hit or before the opponent rolls for damage." It is a fine card, but not so strong that it shouldn't be able to respond to an unusually good to-hit roll.
Aggressiveness x1: Play during the Movement and Command phase. A unit of your choice that will engage/is engaged this turn gets another round of combat after the first round.
I assume both units fight in the second round? If not, this is busted in half. If so, give it some reminder text just to be clear. You can also get rid of the "will engage" language because you can play it after final rushes.
Brutality x2: Play during an attack, before you roll to hit. If you do 3 or more damage to the enemy, destroy the enemy unit. P.S. Don't use this on a "berserked" berserker charging into a peasant mob.
IMO this card is too swingy. I'm not sure it is broken, but I am pretty sure that every time someone plays it, one of the two players ends up hating the game. That's not what I look for in a command card.
Throwing weapons x1: Play on a unit before initiating combat. The unit gets a range of +5” for the duration of your turn. If an enemy unit engages that unit the next round, the unit’s offense is (–1) -1/-1. If the unit is engaged, it may attack any other unit other than units engaged with it within a 5" range (no additional range granted though).
I think "play during your movement and command phase" is a fine template for this. Cool card, though the wording needs a bit of work, I like the idea.
Intimidate x1: Play before or after combat, in the pre-combat courage phase or post-combat courage phase. Play on an enemy engaged with one of your units. If the enemy unit has lesser health than your unit, it takes a rout check. If not, its courage gets –1 permanently.
This is another card that I'm not sure is broken, but I am pretty sure will lead to un-fun most of the time it is played.
Reckless Fury x1: Play during an attack, before any other command cards are played. Neither player may play any other command cards during this attack. If you fail to do any damage during the attack, do one damage instead.
This might be too good, but I like the idea a lot. My guess is it could be tweaked to something fun and cool.