Natural armor and stacking

I've been searching around for some guidance on how to determine how base armor class works with respect to natural armor. The one bit of guidance I can find on the forums (from a few years back) was this quote from Alex:

"Natural and physical armor stack, provided that the physical armor can be fit over the natural armor. If the result is an ungodly number, you might consider a less-high AC combined with some form of damage reduction (such as the mummy enjoys). That is definitely up to the Judge's discretion."

But after re-reading the section on Thrassians, which are effectively monsters as PCs, it strongly implies their base armor from hide should only be applied when they aren't wearing any additional armor.

On the other hand, the rules for barding (horses, etc) seem to suggest that armor should stack. That is, a horse has base AC of 2, and leather barding (AC1) should bring it up to 3, not leave it stuck at 2 (or drop it to 1 somehow!)

Is there an officially "right" way to figure out what happens when you put additional armor on a monster, or is this still basically judge's discretion? I think the idea of stacking make sense in most cases, but I don't want to end up with a weird situation where Thrassians are either (1) ridiculously superior to other fighters, or (2) following a different set of rules than all other creatures in the game.

Where does it say their armor shouldn’t be stacked?

The Thrassian Gladiator class (PC page 42) suggests it stacks; “If the character wears armor, this can further increase their base AC.” The race description doesn’t mention it one way or the other.

Personally, given the XP costs and stat requirements of the Thrassian Gladiator, I have no problem with them having +3 AC over other fighters. (They aren’t even a competitor for highest AC in the game, although admittedly they might be if you don’t count bracers of armor shenanigans with non-armor classes.)

Also, as long as we’re talking about thrassians, I’ve always wondered why they need to wear chain or lighter to use their natural weapons. I don’t think that’s a general rule, and the Fangs and Claws custom power doesn’t mention it.

Currently the description says "Thrassian gladiators are bred to have thick, scaly hides that give them a base unarmored AC of 3 instead of 0. If the character wears armor, this can further increase their base AC." It's the sort of phrasing that's probably obvious if you already know what it's supposed to mean, but doesn't decisively answer the question, since it allows multiple interpretations ("Sure, it's an increase, but does plate mail increase me to 6 or increase me to 9?") I took the use of the word "can" instead of "will" to mean it was only possible that armor might increase it, not that it definitely always would.

What beats them in armor class? Currently I'd say that the Companion rules give a level-4 Thrassian class the possibility of an unbuffed permanent AC of given by 9 (plate+3) + 5 (Thrassian) + 3 (DEX) + 4 (shield+3) + cloak (+3) + ring (+3) = AC 27. I can't see an easy way to top that -- and certainly not to be so much better that it isn't even "competitive". And it's all available at any level.

Hmmm, I'm not sure I want to know the answer. That will just mean that the half of my group that currently insists on playing only lizards will now insist on exclusively playing whatever beats them by 1 AC. (*grumble* powergamers *grumble*)

Oh, and feel free to morph this thread into "how to dynamically balance Thrassian classes through campaign design", since that would be equally useful to me. Currently, they eat most of the random encounter tables for lunch. (Literally. They're always super-smug about how they can use any random beastmen corpses as their rations!)

It is actually definitely competitive, I misremembered what the number was and thought bladedancers could crack 30+ buffed.

But that said, a Thrassian-4 does have the highest permanent AC, but a Gladiator isn’t Thrassian-4! They only get +3 AC racial.

If you allow Bracers of Armor to stack with Flesh Runes, a high-level Dwarven Fury can get AC 7 (bracers) + 6 (flesh-runes) + 4 (shield) + 3 (Dex) + 6 (cloak and ring) = 26
(actually, 27 for weapon and shield fighting style proficiency, but your example was missing that). This is 1 point above the gladiator’s max AC, and only one point behind Thrassian-4.

Buff spells can bring it above that, but yeah, the 24-28 range is about the top end unbuffed. (Note that I count self-only spells as class abilities, like Shimmer, since you can’t just stack them on the fighter; without putting it on a custom class list, only bladedancers can get the +2 AC bonus from Shimmer.)

As far as how to balance them through campaign design: Enforce that reaction penalty. Everywhere. They may be the best at slaughtering monsters out in the wilderness, but they get less money for their loot, they can’t get henchmen to follow them without planning to betray them, they can’t set up a merchant empire or hire mercenaries. Basically, everyone hates them, and they should transfer that hatred to the party too, if the party lets them run around free and be valued party members.

In my campaign, bracers of armor are mage items, so armor restrictions stick with other classes for the entire career.

As far as how to balance them through campaign design: Enforce that reaction penalty. Everywhere. They may be the best at slaughtering monsters out in the wilderness, but they get less money for their loot, they can't get henchmen to follow them without planning to betray them, they can't set up a merchant empire or hire mercenaries. Basically, everyone hates them, and they should transfer that hatred to the party too, if the party lets them run around free and be valued party members.

If I keep the stacking armor, then there's no question that balance becomes a major concern. At this point, the game is becoming "Lizards, Dwarves, and Elves", which seem like the only popular classes due to survivability (providing the highest armor variant for each essential party function). Currently I have 4 Thrassians, 2 elves, and 2 dwarves, out of 10 players. Currently, both the henchmen are lizardmen (for which the reaction penalty is reversed!)

At the moment, everyone is so far from civilization that it's hard for reaction penalties to have much bite. The regional cities are chaotic and are already pretty hostile (there are multiple kill-on-sight warrants issued for various characters), and at this point its easier to acquire food and supplies by killing chaotic merchants (the party took down a huge caravan two weeks ago!) than by dealing with them.

On top of that, it's relatively easy for the party to invent ways to conceal the offending party members: disguises, illusions, giant cloaks, or just stashing them inside of one of the caravan carts they've captured, under a tarp.

Other approaches to balance:

  1. Generally tougher encounters that outlevel the party by a few hit dice. This tends to give the lizards a challenge, but kills everyone else lightning fast. Also, I have some philosophical distaste for automatically scaling everything based on the party composition, which feels simulationally contrived.
  2. Fights that emphasize movement speed, like archers in an ambush position that needs to be quickly assaulted. These are a bit hard to set up, and if I give the archers powerful magical bows or thrown weapons to have a respectable to-hit, then the party can sell them for lots of money, which creates inflation issues. Also, the last time I tried this, the party just blocked the archers with a Darkness spell and then cast spells on any party members without infravision to let them see in the dark. Good strategy, when your party is half gnomes/lizards.
  3. Salting random encounters with high-level mages that selectively target Thrassians with save-or-die magic. This is harsh, and pretty obviously a contrived "screw-you" move, so I'd rather do it as a last resort. Also, this just pushes players toward using dwarves instead, for the Saving Throws. The real balance I want to fix is relative to the standard Fighter.

At the moment the last option feels like the least objectionable. But I'm anticipating lots of complaints from players.

For fights involving movement speed, surely horse archers would be a nightmare for a slow party. Especially because they can skirmish and it's quite difficult to use single spells to remove them all. Or if you're feeling particularly evil then flying archers are always good. Perhaps the owner of the caravan they attacked either is/hired a mage to deal with these upstart half-breed scum.

I have an idea there are systems that split the difference.  Say you put armor or barding on something with a tough hide, it gets some improvement, more than just taking the better and ignoring the lower, but it's not a simple addition either.  So, say a -1 or -2 off the scaly hide 3, but always at least a +1 for putting on armor.

Or, speaking of damage reduction, there's a little twist I like that I first encountered in the writeup for elephants in Qelong.  They ignore damage totals of 1-3, but it's not DR in the 3e sense, damage totals higher than that aren't reduced at all.  Say Thrassians in armor use the armor's value but ignore damage totals of 1, or 1-2; it's a real benefit, especially at low levels, but it's not game-breaking in the same way.

I agree the OP's got a real concern.  I forget now who and where, but someone had a blog post proving with Science! math that pushing a high AC higher still provided more benefit than pushing a low or middling AC up by the same amount.

I agree the OP’s got a real concern. I forget now who and where, but someone had a blog post proving with Science! math that pushing a high AC higher still provided more benefit than pushing a low or middling AC up by the same amount.

That’s 100% true, AC has increasing returns. Each point of AC reduces the target’s hit chance by 5%, which is a bigger reduction in hits per attack the more AC you have.

That is, if you go from 50% hit chance to 40% hit chance, (.4/.5) = .8, so that 2 points of AC means you get hit 80% as often.

If you go from 20% hit chance to 10% hit chance, (.1/.2) = .5, so that 2 points of AC means you get hit half as often.

It does eventually flatten out when the target values become 20+, of course. If I have to roll a natural 20 I don't care if your AC is 25 or 40.

This is exactly how I've been coping with the Thrassians and lizardmen henchmen during the last couple sessions. I've used huge groups of 1st level mooks (which arise naturally in outdoor encounters, without having to fix anything "by hand"), and then having them exclusively attack the high-armor targets. When you only hit on a natural 20 with level 4 characters, a group of 40 level 1's is actually a better challenge than a group of 10 level 4's. It's another one of those things that "looks crazy" the first time you see the original edition tables, but now seems very sensible. (Of course, all the mooks have to share initiative and stay in formations for it to remain manageable to run!)

The problem is that when situations arise where they want to attack a low-hp target, that target vaporizes almost instantly. This makes avoidance spells that do something more than just add AC (like sanctuary or protection from normal missiles) very valuable, and it means that any time the heavies start to go down, it's going to quickly become a tpk.

Definitely! 

As far as soft targets, key rules to note here are that attackers can't easily move once engaged, have to use ovverrun to get past opponents who have engaged them, and can't fire into melee unless they have specific proficiencies (and even then at a steep penalty). ACKS intends to makes it fairly difficult to snipe at soft targets if the heavies are defending them. 

What this does mean is that, by far, the most dangerous situation a party can find itself in is to be engaged at long range by a large number of mooks with missile weapons. This is also by design. It seems to reflect the fantasy literature fairly well -- you'll often see a hero be invincible in melee, but taken down by masses of arrows from afar, and heroes tend to be most likely to surrender when surrounded by ranged attackers.